To me it sounds like its coming more from the top and and front of the engine, but I cannot pinpoint it. I unplugged the vacuum advance hose today while it was idling in drive, and noise reduced to how it sounds while its idling in park, faint but still there.
Also, after observing under the hood for 5-10 minutes, my clothes really smelled like exhaust, starting to lean toward exhaust manifold leak.
They do that if the plate is dented OR the torque converter is about to snap it's neck.
I am pretty sure it has someting to do with the flexplate touching the steel sheets that cover the lower gap of the bellhousing.
ANjo
The transmission was rebuilt less than 2 years/15,000 miles ago. I'm not saying its impossible, just seams unlikely. It doesn't sound to be coming from the transmission either.