Ljones
Try fresh batteries.
If you move the ear-cups on your head, squishing them in and out or shake your head violently you send out a pressure wave which the ANR pick up senses as and tries to match. Due to the extreme pressure wave the ANR works overtime and sends out a warbling tone trying to match it. If the batteries are low but not yet indicating low by the alternating green/red flashing LED and blue tooth is selected on it will kick the blue tooth off.
I just re-tried mine as this warbling sound was common when I moved the ear-cups unfortunately I couldn't replicate it, I did note that as I squished the ear-cups the green flashing LED went to green/red flashing indicated that it was drawing a size-able current draw trying to match the induced pressure changes.
Either way not a problem in flight unless you get into brawl with pax or #2 or #1 depending on your circumstance.
Tip: sound quality better through plug in lead than blue tooth and batteries last a bit longer. Enjoy the sound quality!
M