Quote this form Ian of the other forum. He said this is from Toshi Terada's response about the E-M5 hum.
"OM-D doesn't have a fan. The noise comes from new IS mechanism. As you know, the image sensor unit keeps center position in image circle always.
Even if the IS is off, anytime image sensor unit is controlled to be at the center position. The sound comes from the vibration and changes by each control mode. It does not affect the sound in recording movie.
Because the image sensor unit is floating by electronic magnetic power, without battery power the unit moves down from center position of the image circle. You can see the image sensor moves a bit down, when you stitch the power off without lens."
Amin, what those guys are saying is correct imho. As soon as I read the title of this thread I new it would be something to do with the stabilisation coils and was just about to mention Electromagnetic flux myself. I've dabbled in electronics and have made a myriad of high voltage machines and coils do indeed make sounds. The higher the voltage the higher the pitch. Young or undamaged ears can clearly here the high pitch whistle of the step up transformer in and old CRT display or Tv. Not far down the road from us the overhead powerlines hum from the vibration of the wire strands.
My plasma tv "hums" when on. Standing in front of it its pretty noticable in a quite room. Sitting 10 feet away I can barely notice it. Once the volume is at a normal level, I can't hear it. My 20" CRT when on made a faint high pitch hiss. Probably on the edge of normal hearing.
In some of our products we design, some of the FETs chirp or hum. Some of them are high power, though.
The only way I'd see this as a HUGE issue is if I were doing video and it come through onto the video. I take pictures though, I don't care if the camera makes noises.