For a while now my 85 IROC has had a rattling problem in either the drive shaft or transmission. The transmission was fully rebuilt and had a "Jr." shift kit installed. THEN, the forward clutch piston "snapped in half" (according to the shop), and the transmission was re-rebuilt (this was all about a year ago)Every time I am in gear and at a stop the drive shaft rattles pretty badly. Its not constant though, it will rattle for a second or so, then stop, then do it again until I start moving. It will also rattle as my car idles down while I'm in park. I had it put up on a lift once - the noise is definitely coming from underneath/around the transmission plate.

When I had the engine rebuilt I had them check the flexplate for me for any cracks, but it was fine. Any other ideas? Thanks for your help!

PS: I did a search on this and came up with 1 topic that seemed pretty closely-related to mine, but that was over 2 years ago, and not the exact same problem