Hey RO'ers, I am looking for advice on how to get rid of the humming noise coming from my monitors. I don't know if it is because the monitors are too close to the rest of the equipment or if it is something else. I notice that when I unplug the connections from the mixer and move the patch cables away from the mixer the humming stops, but as soon as I place the cables near the mixer or plug them in for that matter they hum (like feedback). Can anyone guide me in the right direction as to how to get rid of this annoying sound? I have the following equipment in my project studio:

Digidesign M-Box
Yamaha MG12/4 mixer
Roland DS-50a reference monitors
Kawai FS-690 keyboard (for midi control)
Yamaha PSR-172 keyboard
Lacie 160 GB firewire external harddrive
Maxtor 80 GB usb external harddrive
Midisport 2x2 midi interface
Gateway M305x notebook computer w/ 512mb and a 2.40 Ghz processor
MXL 990 condenser microphone
MXL 991 condenser microphone
NAXA NX-982 dynamic microphone

I have the line inputs of the Mbox connected to the mixer through the alt 3-4 bus, the line outputs of the Mbox connected to the line in on the mixer, and the monitors connected to the stereo outputs of the mixer. Please help me get rid of the annoying sound coming out of the monitors. It sounds like when you are trying to tune to a radio station and can't quite get the station to come in. Thanks in advance.