I an SG clone with Stewmac humbucking pickups that I wired. The problem is that the guitar loudly buzzes when either the bridge pickup or the neck pickup is selected. When both are selected there is no buzz.

I've double checked the grounding from the bridge and the rest of the circuit.
Replaced the capacitors.
Verified that nothing is touching that shouldn't be.
Both pickups seem to have a good DC resistance (8.5K for the bridge and 7.9K for the neck) and 4.7K when both selected)

Is there anything else that I should look at?

This problem is happening on two different amps.