Scooter,
The good news is that you are getting at least some sound to pass through the circuit, so we know it seems to be working on some level. This problem sounds like a bad connection somewhere…like a bad solder joint in the audio path. The volume knob is off in the counter clockwise direction…is it behaving that way? I suggest you re-flow your solder joints again to make sure everything is connected the way it should be. Another possible cause could be the signal is partially shorting out somewhere, possibly against the back of one of the pots when the circuit board is installed in the chassis. Make sure the pieces of paper don’t have any holes in them and nothing is poking through.
Good luck.
-Brach