I just got done putting a new motor in and something is squeaking. It's a stock 350 with a one-piece rear main seal. I've ruled out the belts. It comes and goes and only seems to start after it has warmed up quite a bit. It won't squeak under load, just at idle or light cruising speeds. I'd take in into a shop and have someone look at it, but it's so intermittent they'd never hear it.
I did some searches and found that it could be a cracked or loose flexplate, a transmission front pump problem, or a main bearing.
This got me thinking...when I replaced the front seal on the transmission I noticed some scoring in a few places just inside of the seal. Is this a bearing? Could it be making the noise? The snout on the tc seemed fine when installed.
I wish the noise was more regular...I'd unbolt the tc, start it up and listen for my squeak/squeal.