tranny sounds at 60mph HELP!!!!

I just bought this truck today and I was on my way home from the lot and the tranny made made real bad sounds once it got to around 60 MPH. It sounded like ball bearings jumping around inside the floor by the tranny right where the shifter is. It is very loud and scared the crap out of me when it came on. There isn't any vibrations that come along with the noise and the tranny doesn't slip or anything, just very loud - sounds like somebody dropped some metal ball bearings into a tin can and is shaking it real hard. Does anyone have any ideas?

Thanks

Harley

Replaced the U joint and problem fixed.