General Maintenance & Repairs - Bad vibration

I posted a thread on this a while back, but it's getting worse. I have a very noticeable droning/vibration throughout the car when the engine is at 2500rpm. it makes the dashboard and the center console rattle like crazy but, like I said, only at 2500rpm. From the outside you can hear it, and from the inside it's even worse (unbearable with the windows up). I thought it was from the exhaust, but I can't find the exact location... it seems to be coming from the entire driveline. I've crawled under it several times and I don't see anything rubbing or banging. I've heard every diagnosis from a bad TC to "piston-cylinder wall clearance issues. I'm at a loss. Any ideas/thoughts/help would be greatly appreciated. :bang:

First you should pull off the serpentine belt and see if it still does it, if it does then unbolt the torque converter and see if it still does it. If you still feal vibration with no belt or converter hooked up...then guess what, engine time! If it goes away with the converter disconnected...then guess what, converter time!