High pitched "whine" in a AC powered circuit

[gmr1]

Have a rack mount vibe unit on my bench that runs on 12v AC. It's got a very audible high pitch whine when turned on (which gets louder when raising the volume level). Tried isolating wires, using a different adapter, different outlet, but no luck. Any suggestions on what common remedies are in these situations? I'm not too experienced in AC powered circuits so any suggestions would be greatly appreciated. Thanks!

[Paul Marossy]

I assume the unit runs on DC supplied by an isolation transformer connected to line voltage? In any case, it sounds to me like there is an oscillation in the circuitry somewhere that is finding it's way into the audio path.

I had a similar problem on the first Shaka Tube that I built. A whining noise was finding its way into the bypassed signal because it was sitting there oscillating when in bypass mode. I'm not sure how that happened as it was wired true bypass, but after I changed it to a grounded circuit input scheme, the problem went away.

What IC chips are inside of it? Are there any charge pumps in the thing? Sometimes those can make an audible whining noise, too.