Like some others said, check all the connectors, to see if you knocked something loose. It would also be a good idea to reflow the solder on the amp PCB, and the Cheap Squeak PCB.
-Mark
Not sure if this pertains to you or not- but-
My Spy Hunter had a hum/ hiss that was a little loud, not too bad, but noticable when you were-not playing. The hum/ hiss would go away if I unplugged the Cheap Squeak PCB. So naturally I looked into that PCB, I replaced the Caps, and the pre-amps, but no dice. Turns out, I decided to swap the power supply from my Demolition Derby, and the hum/ hiss was gone. I put the power supply in my Demo Derby and it was fine. Spy Hunter didn't like it for some reason!