Denso whine

[aerhed]

I just swapped alternators in the 10 to get rid of a slight whine and the new one does it also. So, I've tried this on 4 denso type alternators since. All 4 same thing, when you apply power to the regulator they make a little high pitch whine (F above middle C). They do this sitting still or running and I can hear it from 10 feet away in a quiet hangar. The noise that carries through the radios matches it in pitch and does not vary with RPM. I've been able to filter it out of the radios, but I can still hear it outside the plane. Anyone else notice this?

[RV6airplanePilot]

I tried 2 alternators and find the whine speeds up with the rpm. I can make it go away either by turning off the alternator field or my PMA6000 audio panel. My regulator is the old Ford solid state. Have a new backup regulator; tried it with same results. Never tested it by listening outside or with engine off, but with headset on and electric on before startup I don't hear any noise. Have used 2005 Bose and Zulu headsets with same results. Found the audio panel ground wire broken last month, but when I reconnected the ground wire the whine did not get better, but the general sound quality of the intercom did. My alternator came out of my old RV6A and had no whine in the old plane. New brushes and polished slip rings, no evidence of diode failure. Conclusion: I need help too. Could something be burned out in my PMA6000?
Thanks,
Dale
RV6a 2 Icom A200's and PMA6000

Revised to add info June 3

[aerhed]

If it changes with RPM, that's a different thing. I think thats usually diodes, brushes, or unfortunate wiring. This is different. You can hear this when you turn on the regulator even without the engine running and its a constant pitch & amplitude.