Re: Hum X Hum Killerer
I've had bad ground loop problems with EMG's (SA's). It's aggravating for sure.
I'd just chalk it up to different electrical components in the guitar causing the loops to pick up different frequencies - I'm thinking somewhat similar to the effect of a tuner know on a radio.
IMO, its best to work on eliminating the ground loops. Use the cheater plug suggestion I mentioned at your own risk - I know enough about tube amps to be dangerous, so ask an expert. ;-)
Use a Pedal Power, if you have a rack, use humfrees/shelf washers, modify your signal cables first. I've read it is possible even in a complex system to eliminate ground loops without going to cheater plugs, just never had to go that far.