Help! 72 vette undercarriage noise

[mrbvette]

I get a "thumping noise" from under the vehicle when I turn to the left. It goes away after I drive it down the the road; not far. I let it sit, overnight for example, and it starts again. I have had the entire suspension including the rear differential rebuilt prior to this noise. The only thing I did not change were the wheel bearings. The mechanic who did the work said they were fine at the time. This was less than 100 miles ago. Any ideas