I had a hum coming thru my preamp from a little 12V transformer used to power something unrelated that was too close to the pre.....look around the unit for anything that might cause the problem. Also turn off any dimmer, automatic light sensor and flourescent fixtures anywhere in the house. (auto light sensors and dimmers can create havoc).
Grounding Hum
I recently got a new TT for Christmas. It's an MMF 2.2 LE. I think there's a grounding problem or something because there is a slight buzzing noise present. I looked through past threads on the topic here, but nothing seems to fit this situation. I've checked, and rechecked the connection between the TT, and the preamp. I've even used a Fluke voltmeter to check for continuity between the two. I've checked the headshell leads to the cartridge. All is well. Maybe it's the ground wire connection to the turntable itself? I've run out of options. Any ideas?