[1967gto1]

I have been noticing that after driving car for a while there is a chatter/clanking sound coming from the rear end. It only does it when the car is warm. When I come to a stop at a traffic light it is really noticeable. It is also noticeable driving at slow speeds (15 mph or less). My car is stored inside the basement when not being driven. When I want to drive it, I put it in neutral and push it out. I don't start the engine. I noticed when I do this there is a binding feel when it's being pushed out. I took the car to a local shop and they put it on a lift. I put the car in 2nd gear and the mechanic showed me the drive shaft was not spinning true. Both rear wheels also did not spin evenly. Could it be that my whole problem is the driveshaft is out of balance or bent and not a problem with the rear end. The car has a posi rear end. Any help would be greatly appreciated.