trustnoone:
Its back to doing it again!! NOOOO =( =( =( =( =( =( =(
!!!!!!!!!!! 
Any socketed chips on the board? Remove and reseat them.
Inspect for bad solder joint. all it takes is one to create a noise element.
The USB connection, the one component that you can't change is the board connector. Inspect that.
And when I say inspect I mean magnifier, from every angle possible.