I have a 350 with a tpi setup on it, i rebuilt the engine last year, and when i put it away it was fine last year, i started it up this year and it idle fine for like 10 mins then started making noise, similar to a cracked flywheel. it does not sound like a bearing noise its not as consistant, and it sounds more tinny, with a stethascope it sounds the loudest in between the bell housing and the engine.... I pulled the trans, and ran it and it still makes the same noise, but as soon as you shut the engine off and started it again it goes away for a while???? also when its not doing it you can rev the crap out of the engine and it sounds fine. Also when it was running with the trans out the flywheel looked like it was not streight, like it might have been bent a bit? could this cause this, (the flywheel had no evidance of any cracks) im stumped?

 

It's not unusal to have some run out int a flex plate. Look at your starter and see if it may need to be shimed out some.