Need help identifying 99 F350 rattle.

[gparrow]

Since it's gotten cold here my 99 F350 auto trans has been getting a rattling noise on and off that sounds like it could be coming from the trans/Bell housing. I know this may sound weird but it usually starts up after a hard acceleration or hitting a bump in the road (like something is coming loose). It sounds kind of like a dime in a dryer, but then eventually will just go away, then may or may not come back for several minutes. Other than the noise the truck runs fine, shifts fine and there is no slip. Anyone have any ideas?

Greg