Only times I have experienced a warble like you describe using ANR has been either the battery is dying or flying in an open cockpit where the ANR is having a hard time compensating for the wind buffeting.
Hi everyone.
I've experienced a very loud low frequency, warble is the best way to describe it, with many ANR headsets and in many makes / models of aircraft on both pilot and copilot sides. This interferes with the ability to hear communication and can be very annoying, I am not sure if it can cause ear damage or not but it can be disturbing.
I would think that this is the reason why the message is being sent out. TV
You're both very close to the potential answer. Yes, you can get an "ANR vibration" in one or both ears in a few environments.
IF you have a headset with external sample ANR (i.e. Bose, Lightspeed, Sennheiser) you will get the speaker vibration or failure of the ANR any time you're in an open cockpit environment or anywhere active air is passing over the earpieces. Yes that includes the cabin air ports pointed at your head. hint, hint.
So while you'll get what you think is a "stronger" ANR in quieter environments, it's actually the exact same protection, but those headsets are compensating a lack of passive noise reduction with high cone deflection sound waves. (A rapidly moving speaker delivering extraneous pressure to the ear drum making you feel like it's working harder) So you're able to hear it when the ANR is disabling itself.
You can also get it in any ANR system with a depleted battery. You will most likely notice the issue in both ears, rather than one side or the other.
IF you have an internal sampling ANR system, (i.e. Squawk Shoppe, AKG, Telex, Pilot, David Clark) you can still get the ANR vibration, but it will always be from a loose ear seal or a low volt battery discharge. This also occurs in the external ANR systems.
Since you are confident that the earseal is not the problem, my next pathway would be cabin air ports pointed at your face/earpiece. Hopefully that solves the "warble". I like that word description. I'm going to use that!