Does the buzzing occur in all switch positions and volume/tone settings? Before anything else, just give each wire/join a little prod/jiggle to make sure there isn't a dry/bad solder join somewhere. If that doesn't find the problem, then it's time to divide and conquer...
If you want to do a quick test, disconnect the grey switch wire on the volume pot and also the output wire from the jack on the middle lug of the volume pot, and then temporarily join those wires together. That will remove both the volume and tone pots from the circuit and have the switch going straight to output (assuming you still have the components on the control plate). If it no longer buzzes then you'll know it's one of the pots causing the problem, most likely something shorting to ground or possibly a cooked component from overheating while soldering.