2008,Loud banging from rear suspension of Ford e350 cutaway van single wheel rear not dually.

I have a e350 cutaway 4×4 shuttle bus. It has leaf spring rear suspension. Whenever I go over little bumps or changes in road level (i.e. going from dirt to pavement or construction) there is a loud bang that sounds like something hitting the frame of the bus. I currently don't have much weight over the rear axle and was wondering if it had to do with that or possibly a bump stop? The rear suspension has not been modified besides a lift block.

My car has 95000 miles.
My car has an automatic transmission.