Hello.  After driving my 1969 for  approx 20/30 mins  I hear a thumping sound coming from the rear of the car, when I accelerate from a stop and turn the wheel.  Any suggestions?  Anyone know a good mechanic in the Norfolk, VA area that knows how to work on C3 corvettes?  Thanks Bob in Suffolk,VA

Fantomworks are in Norfolk and love working on Corvettes -- their shop always has a lot of Vettes in it.

They used to have a TV show that was very interesting.  Dan Short and staff do meticulous work that they are proud of.

Their web site is: fantomworks.com

Could possibly be trailing arm bushings. How is tire ware?  Also the nose cushion on the differential brace could be worn and loose. 

The nose cushion was my first thought too.

When you say  a "thump", is that a dull thud, or a harsher, almost metallic banging?

If it occurs when you are turning my thoughts would a U/J failing, or the diff needing a fluid change.   

The latter becomes evident when the diff warms up a little and the car has been running in a straight-ish line for a few miles.   It'll normally "crack" a few times (the posi clutches "stick") then settle down until you do another long straight run.  Drain and refill with good mineral gear oil and two bottles of the GM Diff additive.

My '75 roadster 3:08 diff positrac did that while making a left turn. My shop replaced the fluid with new positrac gear lubricant.  It resolved the issue!

My friends '68 roadster 3:08 does the same!

Changing the diff fluid with a positrac lubricant may resolve your issue. 

Hope this is helpful!

I changed the fluid in mine. But only after a bunch of other preventative repairs. There was no drain hole in mine. So.. I drilled and taped the bottom. Total drain, flush with carb cleaner and kero. Put a flush plug in it. Filled with 80 oil and two pints of GM positrac fluid. Did about 10 minutes of figure 8s in a parking lot, good to go. No problems! 

I think bad u-joints will make a chirping/squeaking noise when turning in a circle.  Don't think they clunk.

I towed a boat with my '78 and eventually they started chirping and got replaced.

If U joints made a clunk, they would be on the ground under the car. A quick peek would tell you if they were bad. Check all four for looseness or missing parts. They are not really hidden. 

Every spring after the cars sat all winter this was an exercise that all would get before any serious driving took place - forward and reverse.  Was fortunate that no one ever called the local law enforcement kids for my doing "crazy stuff" in a parking lot...!!!