squeak squeak squeak!?!?!?!?!

[toddtheodd]

So.
Specs are.
72 custom 10 deluxe lwb.
350 engine, 350 trans, 2 piece drive shaft, 3.08 gears. Coil springs.
No a/c. :P

This just started yesterday, and it is not a "everytime" type thing.
My truck started squeaking on me under acceleration. It is at moderate acceleration only. WOT and DMD (DMD = Driving Miss Daisy) doesn't cause the squeak.
It does not squeak in neutral. Neither at the rpm nor at the mph. Only in gear. Which leads me to believe that this is not an engine thing. When I rolled down the window it sounded like it was coming from either directly under me to the rear of the truck. But we all know that sound locations can be deceiving at 40.
When I say that this does not happen everytime, I mean that I drove all the way to work today, and all the way to a resturant for lunch without any noise whatsoever. But while leaving I had to make a sharp left turn, and it started squeaking and continued to squeak (under moderate acceleration) for a little while, then eventually stopped again.

What the hell is this squeak. It is loud enough to be heard over my exhaust which sets off car alarms.

Also noticed that when I take a hard turn I would feel something go "thump" under the floor board. Could this be a related issue?

Any help would be great as this is my daily driver and I can't have it be down.

Todd