Rattling noise upon starting and then louder rattling at idle if load is placed on engine such as A/C

My problem started as a rattle at idle when my A/C was on. Sometimes I get the rattle simply with fan on at idle or even just a bit with fan off, especially at a low-speed turn. There is also a rattling noise at start-up. These problems come and go to some extent, but have gotten worse – one step forward, two steps back. The noise at idle with the A/C on now is very loud – obviously I don't run it at idle.

I replaced the idler pulley and belt tensioner assembly – no help.

I am thinking perhaps the power steering or A/C pulley or the crank pulley or damper. More serious would be torque

Experienced mechanics share their insights in answering this question :
Hi there. Given your mileage and your maintenance of the idler pulley, your problem is likely worn/weak hydraulic lifters (or other valve train wear) or the timing gear set. Starting the engine briefly (less than 30 seconds) without the serpentine belt attached, will eliminate noises from all accessories if the problem is with one of them. I would recommend having the engine inspected in person by a professional so that the rattling noise can be diagnosed and properly corrected.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

Check Your Motor Mounts

If one or more of them wear out, your engine or transmission will be less secure and you may notice a rattle that doesn`t go away when you start driving. While an unsecure engine or transmission can more easily be damaged, replacing any worn or broken mounts is a relatively simple car repair.

A Rattling Noise from the Engine When Accelerating

Noises coming from the engine when you are pushing on the gas could be caused by a loose or weak timing belt, chain tensioner, cracked flywheel, or a broken flexplate. These issues will only get worse over time, not better.

The most common reasons a Dodge Grand Caravan has a rattling noise are the ball joints, struts or strut mount, or a problem with the sway bar links.
There are several causes for the engine to rattle while idling. With your car, the heat shield or an under engine shield is most likely. The other causes are the AC compressor clutch, idler pulley, or belt tensioner.
If the rattle lasts 2 -5 seconds then goes away, it may be related to the timing chain tensioner in the engine. If the rattle comes and goes, it could be something as simple as a loose exhaust system heat shield. If it is constant at idle, it could be loose waterpump pulley bolts.
The reason timing chains can be noisy on start up is either the pressure in the oil charged tensioner is bleeding off, or there is extra slop in the chain system that the tensioner isn`t design to take up. Dirty oil can lodge debris in the tensioner that will keep the check valve open bleeding off oil pressure.
Rattling Noise – Once your catalytic converter becomes older or damaged from fuel mixtures, the honeycombs on the inside can begin to collapse and/or break apart which will cause a rattle to occur.
What does a bad catalytic converter sound like? Often, a clogged catalytic converter sounds like a rattling noise is coming from under your vehicle and engine when you`re starting, idling or driving. Excess heat or damage in the converter can break apart the honeycomb materials, resulting in the rattling noise.
The most common reasons a Dodge Grand Caravan has rough idle are a vacuum leak, an issue with the spark plugs, or a problem with the ignition coil.
While a rattling noise can come from several different places within the transmission, you will want to start with a basic transmission fluid service changing the fluid and the filter. During this process, the bottom of the transmission can be inspected for signs of metal shavings and more serious issues.
Worn Crankshaft Bearings

Sometimes the smooth movement of the pistons inside the cylinders is disrupted because of a mechanical failure. Older engines can have worn-out crankshaft and connecting rod bearings, which cause a knocking sound when the engine is idling.

Rattling from under your car– This can be caused by loose parts such as your exhaust system. Squealing wheels while braking– Causes range from small, such as dirt on the brake pads or rotors, to serious, such as worn pads. Brake noises are safety issues and require immediate attention.
Rattling on cold start up is usually an indication of a timing chain issue. Timing chains synchronize the crankshaft and camshafts so they rotate at the proper time for the engine to run properly.
A Rattling that seems to be coming from the front of a car engine could be an indication of a timing belt problem.
Knocking Sounds

If the timing belt tensioner is loose and the timing belt is getting stretched out because of this reason, you will continuously hear knocking or slapping noises. This happens because the loose timing belt hits several parts inside the timing belt cover.

The noise is normal, and is created by engine pulses being amplified through the light-off converters. Do not replace the converters unless loose internal components are found.
Reduction in Engine Performance

A failing car`s catalytic converter will create a significant backpressure that lowers your car`s engine performance. Whenever this happens, you will notice your car shaking frequently, and if there is a sudden outburst of pressure, the engine can stall even when on the road.

Well, you`ve definitely done your homework! Yes, a bad catalytic converter can cause a rough idle. This is because less exhaust will be able to escape, in turn reducing the amount of oxygen that can enter and combust in the engine. It`s best practice to replace the catalytic converter sooner than later.
Tire issues: The most frequent causes of a vehicle shaking while driving stem from tire issues. Tires begin to behave differently when worn or out of balance. Tire replacement, realignment, and rebalancing are common solutions.
Any unusual shaking or vibrating forces coming from the engine is cause for concern. It could be something as simple as old spark plugs producing an uneven power delivery, it could be something serious like worn or broken engine mounts, or it could be even more serious in the case of internal engine damage.
This noise sounds like a rattle or whine coming from the gear box, and it`s commonly referred to as “gear rollover noise” or “gear rattle.” While it may seem counter-intuitive, this noise is not a symptom of a problem. The noise is a natural consequence of the vehicle design.
Loud or Noisy Transmission

This is characterized by a high-pitched whining noise, a combination of whining and grinding noises, or a strange gurgling noise. Some of these sounds are worse than others, but all are an indication that your transaxle is malfunctioning.

If you hear a rattling noise while driving, the first step is to not ignore it. The sounds and vibrations coming from your vehicle could be signs of a serious mechanical issue. Seek help from a professional who can find the source of the noise before any further damage is done.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Rattling noise upon starting and then louder rattling at idle if load is placed on engine such as A/C
ANSWER : Hi there. Given your mileage and your maintenance of the idler pulley, your problem is likely worn/weak hydraulic lifters (or other valve train wear) or the timing gear set. Starting the engine briefly (less than 30 seconds) without the serpentine belt attached, will eliminate noises from all accessories if the problem is with one of them. I would recommend having the engine inspected in person by a professional so that the rattling noise can be diagnosed and properly corrected.

Turned on back winow heater and engine made a noise …when lights are turned on engine makes a noise like it can’t take load ….
ANSWER : Hi there. It appears you have more than one problem with your vehicle. The noise coming from engine area with a load on the electrical system, may be a bad diode in the alternator. Continuing to drive the vehicle with a bad alternator diode, may leave you with a dead battery. The hot air coming from the vents sounds like blend door actuator(s) problems. I recommend the concerns your vehicle has, it be inspected by a certified technician like one from YourMechanic to pinpoint the noise and help you fix it accordingly.

Engine tapping noise related to short term fuel trim but only on cold start up.
ANSWER : Has a mechanic’s stethoscope been used to track down the specific location of the noise? There are several solenoid valves in the engine bay that do not run all the time and may be pretty loud once they start, such as an evaporative emissions purge valve and the like. The high fuel trims on one bank sound like you may have a problem on one side with a vacuum leak. A positive trim means air is being added and the computer is trying to add fuel to compensate.

I recommend having an experienced technician, such as one from YourMechanic, come to your location to determine why the engine is making a noise and suggest the proper repair.

Fuel pump engages. Batery good, alternator good volts, jump start helps when wont start. Temp does not matter. Intermittent?
ANSWER : Hello. Thank you for writing in. There are several reasons your vehicle may only start when jump starting. The first and most common is a build up of resistance that is causing you to need a boost of voltage to get the engine started. This may be due to poor battery cables, a bad ground connection, a poor starter solenoid, and a couple of other issues. The first thing you want to do is perform a visual inspection of the starting system. Make sure there is no corrosion build up in the battery cables. You can also check the resistance across these wires and make sure you have a solid connection between components. You then want to make sure the starter solenoid is doing its job. It is responsible for taking the small amount of electricity sent by the ignition and turning it into a huge electrical charge that is strong enough to push over the engine with the help of some gear ratios in its favor. Do some more testing, and stick to the basics before assuming its something seriously complicated.

The engine is making rattling very high noise when you start the engine and constant.
ANSWER : The fact that the oil pressure drops when slowing down or stopping would suggest that the oil pressure is lower at lower engine RPM’s. This means that the oil level volume is low. The oil capacity in an engine is designed to correlate with oil pressure at any given RPM. When it is full, there should always be constant oil pressure assuming there is no oil leaks. I would suggest having an expert from YourMechanic come to your home to diagnose your vehicle and make appropriate repairs to your vehicle.

Check engine on knocking engine milky cap but not in oil change loud knocking noise while driving and cold start up
ANSWER : Coolant leaks can be external or internal. If the coolant is leaking internally into the cylinders or crankcase, that will require a fairly significant repair. If the coolant is leaking externally, unless the leak is at the head gasket or the lower intake manifold, external leaks can be repaired readily. On the engine you have it was really common to have coolant leaks at the lower intake manifold, so common that the gasket there was completely designed and a different repair procedure was specified (higher torque on the manifold studs). To get the coolant leak diagnosed, please use YourMechanic’s coolant leak diagnostic service link. The knocking noise is obviously of concern. Unfortunately, typically, such noise is from worn bearings, connecting rods, and other major components. The noise might be accompanied by low oil pressure. My best advice is have the cooling leak diagnosed in case that is readily resolvable. The mechanic can evaluate the noise and if it is internal the engine will eventually have to be disassembled and rebuilt. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Engine starts but stalls immediately
ANSWER : This may be an issue related to what is called an idle air control module. This is a module that regulates the amount of air that is allowed into the intake system as it is mixed with the fuel before being injected into the motor. When this is not working properly, this will cause the car to stall as you describe. I would suggest having an expert from YourMechanic come to your home to definitively diagnose the stalling issue and make necessary repairs.

Engine occasionally cuts out while idling at a stoplight and occasionally hesitates and bucks upon acceleration.
ANSWER : There is a issue with the fuel delivery to your engine. It seems as the fuel pump may be failing. Check the fuel pressure on the fuel rail and see if there is at least 30 psi. If the fuel pressure is low when the engine is revved up, then the fuel pump is not producing enough flow to keep up with the demand. If there is pressure, then the fuel pressure regulator is not working. I recommend seeking out a professional, such as one from Your Mechanic, to help you diagnose your fuel system.