Hey guys, I currently am havin a problem with my car and need some input plz.

My mustang makes a popping noise or a clunk sound coming from the rear of the car.
I was told and thought myself that the rearend was bad. it needed spider gears. to go the cheaper route i just picked up another 7.5 rearend.
Sound still exsist. '

I need to know what else it could be.

It is very dependable that it will do it switching from reverse to drive or from drive to reverse.whenever the load is shifted. It also does it at random times sometimes. taking off or when road isnt to even.

the mechanic told me i needed new upper bushing on my rear control arms because the go side to side pretty bad. but he said once bolted on to the rearend it wouldnt make a difference. but could it?

thanks plz help out.. willing to answer any questions you may have