1) Does the cartridge even need to be grounded? The two wires come off if each coil
2) doubtful to be causing a hum
3) Seems the most likely to me
4) I would doubt #4 unless the RCAs were running along side of a power line going into the TT.
2) doubtful to be causing a hum
3) Seems the most likely to me
4) I would doubt #4 unless the RCAs were running along side of a power line going into the TT.