Light thump heard under accel/deceleration

[429mustang]

Hey, I think I know what noise your talking about. Does it make a thump sound almost like a quiet backfire somewhere around the rearend? My car usually makes it when I get on it at a low rpm or in 5th gear on the highway. I'm pretty sure it's not the trans mounts, I just had my motor/trans out and made sure everything was tight when I put it back in and it still does it every once and a while. If I get around to it I'll check my driveshaft and shocks, although if it were the shocks I'd almost think it would do it when you push down on the car a few times, and it doesn't. I'm pretty sure it has to be one of the rearend parts, if I find it I'll let you know.