Feedback-Hum... Hmmm... Sound studio....
3-wire circuits, and/or 2-wire circuits of seperate phases will do this too, if equipent is connected/re-connected on the audio side.
Most of the audio guys I used to work for would request 2-wire circuits of both or all 3 phases available at all points, if not only one phase available for equipment. Then they could choose whatever phase sounded best to them. I never heard the difference!
Feedback-Hiss... Hisss... Sound studio....
Electronic noise induced on circuit, could be from anything. Dimmers, LV, or flouresant lighting, electronic amps, TV in the neighbors house - anything. All of the amplifiers could just amplify the radio signals emitted from them. Thats a shielding problem in thier equipment, not yours.
They could also have grounding issues in thier equipment as well. Which could cause both.... I have installed many isolated grounds for dedicated circuits. And on one occassion a "Common refferance ground" which amounted to a #2 back to the main with a ground bar that they could attach jumpers to form different equipment. Also never heard the difference....
