My audi could hear it through her stethiscope too. It’s definately the aids.
Interesting. possibly distortion due to the high gain???
Doc A: As I understand it all anti-feedback all brands systems use 180 degree phase cancellation. The problem circuit wise is to get exactly 180 degrees at exactly the reverse amplitude at the exact frequency.
The problem comes about when the system overshoots any of the negative parameters.
Yes over driving into non-linear operation could cause this instability with the gain flucturating (warble) up and down. Ed
I’ve purchased the Widex Clear 440 Fusion aids after a 1 week trial. They have no warble and music is fabulous and absolutely no feedback. I still need more volume in the telecoil and I hear a snap when doors close - minor tweaks. They’re smaller and seem fragile with the receiver in the ear. Clarity is pretty good and I think will be better when that snap gets tweaked out. These aids were pretty pricey even through HearPO. I paid $2,595 per aid (let’s get the money part out in the open). The Widex rep told me about the Widex Supers coming out soon in the states - more gain and uses 675 batteries. I’m hoping to work out a trade in the future. 
Glad you like them. I have had mine now for a couple of months and no complaints!
No, there are three or four methods in use. Phase cancelling is just one.
I too am in trial on Phonak Ambras and am experiencing considerable warble…sounds like speaking underwater. My audi thought it might be the Sound Recover so he inserted a program with it turned off and I still have warbling/undulating voices, especially with music. I am probably handing them back in next week to trial something else. Audi wants to try next the Widex Clear super power. I have severe loss and wearing BTE with custom molds.
To clarify some of the speculation in this thread:
The warble, or distortion, that occurs with a tonal input to the hearing aid is most likely the result of an interaction between that tonal sound and the feedback cancellation algorithm.
This warbling distortion is often called entrainment. The sound can be heard by anyone listening to the hearing aids. Many sounds will cause entrainment, door bells, some voices, and music.
A hearing aid is more likely to entrain when the system is close to feedback. This means that higher gain fittings that are not well occcluded are at greater risk for entrainment. Moving to a more occluded fitting or reducing gain will reduce the extent of entrainment, it’s unlikely that this will completely eliminate it.
How to get rid of entrainment:
Most of today’s hearing aids offer different feedback canceller settings. Moving the settings from fast to slow, or adaptive to static, or high to low should all reduce the extent of entrainment. Turning the feedback canceller off should eliminate the problem (not the preferred option).
Why does this happen:
In short, the hearing aid thinks that the tonal input is a form of feedback. The feedback canceller identifies the tonal sound and attacks it. Because this is not true feedback distortion results.
Today’s feedback cancellers:
All of today’s leading feedback cancellers use phase (sound) cancellation. Please note that the phase cancellation is far more robust than simply adding a phase inverted copy of the whistle. This is what makes today’s hearing aid fittings (comparatively) stable and allows for an impressive range of open fittings. A second layer of feedback management is gain restriction. At least one company uses gain restriction that occurs dynamically during wear and most use gain restrictions that are placed (and remain fixed) at the time of fitting.
Thanks Research - a very interesting post!!
UmBongo: Gee did miss something in class. Was always under the impression that once feedback occurred, you could of course reduce the overall gain or reduce the gain at the oscillation frequency. But that would have the patient with less than ideal responce. Educate me. Ed