one item you might not have thought of.. flourencent lights are notoriously electrically noisy, turn them off,use incandencent lights another option might be put your equipment on a filtered power line. an UPS SYSTEM SHOULD WORK UNLESS THE NOISE IS BEING GENERATED INSIDE YOUR EQUIPMENT? THEN THERE ISN'T MUCH ELSE TO DO? USING YOU COMPUTER AS THE RECORDING MEDIUM? YOU'L NEED A PIECE OF SOFTWARE TO TAKE THE NOISE OUT, I SUGGEST POLDERBITS.COM, I USE IT TO TRANSFER CQASSETTETAPES TO CDS AND RECORDS(VINYL] TO CDS REMOVES THE surface NOISE AND "scratch TICKS" NICELY "it is used post processing" it also has an equalizer in it.I used mylaptop computer to do the transfers and I had a bad hum, later I discovered the power supply didn't filter the output power leaving a lot of hum, I thought it was a ground loop. addressing that problem, I still had hum. then I removed the power from the computer , to run on battery the hum was gone! I am not familiar with your equipment. from other posts it the problem is in your equipment. That presents a different problem altogether. if you need a mixer, get a battery powered one. Radio shack has one for $33 4 input channel stereo I purchased one to build a recording studio in a briefcase with 2 cassette recorder decks. all battery operated. it worked for what I needed it for. for 3 years.