if the hum only present when the stylus is on the record, this doesn't sound like ground loop, so I wouldn't worry about lifting the ground.
You say you disconnected and reconnected everything - does this include the signal tags to the cartridge connection? If not you may want to try that and apply some deoxit while you're at it.
If that doesn't do it, you may want to see if your cartridge is going bad. Do you have another cartridge to swap out to see if the hum is also there with another cartridge?
You say you disconnected and reconnected everything - does this include the signal tags to the cartridge connection? If not you may want to try that and apply some deoxit while you're at it.
If that doesn't do it, you may want to see if your cartridge is going bad. Do you have another cartridge to swap out to see if the hum is also there with another cartridge?