it could possible be the U-Joint which is a cheap and easy fix. it's connected to your drive shaft.
when you change directions from forward to reverse it makes a clunk sound and there is a slit delay in movement.
it may be the rear tranny mount
you probably need motor and/or transmission mounts
Possibly a worn out universal joint.
Worn out bushing or steering joint probably.
Possibly weak u-joints or transmission mounts
check engine mounts
I am not sure what you mean by rear, but here are some possibilities. It could be bad u-joints if it makes the sound right when you put it reverse it will could also make it when you put it in drive. If you have the automatic 4L60-E transmission and i only heard this once that the reverse input clutch was so messed up that it made a clunking sound.
This happens on my 2002 mk5 fiesta. The front brake pads move very slightly in the caliper, so when you reverse and apply the brakes you'll hear a slight clunk. I had this repaired by ford as my car was under warranty - replaced pads and noise went away.
Most likely a CV joint...could be dangerous... consult a mechanic asap
it makes a bell soundlikea dinnnnnng
the biggest crate motor GM chevy makes is a 572 not a 502