I recently had my oil pan gasket changed on my 1986 camaro iroc z and ever since I picked it up from the shop I feel a thumping in the drivers side floor and I checked everything whole tune up and also transmission mount and harmonic balancer..what could be causing this thumping????

 

I had the same thing with mine after replacing trans seal, waited about a month hearing the sound and had it up on a lift. Mine was the shifting bolts> they never tightend down the bolts where the shifting connects to side of pan. fixed now!