These headphones have been working fine until about a week ago when upon powering up, the right ear cup blasted a high pitched whine when placed on my ear which lasted about 10 seconds.  Once it had finished, the headphones worked normally.
Now every time they are powered off and then powered on again the feedback whine returns for 10 seconds or so before fading out (and again allowing normal usage).
I have had to resort to putting them on and quickly moving the right cup to the side so that I'm not deafened by the high pitched sound and then once it has finished whatever it is doing putting it back and using the headphones.
Only other info I have is that prior to the whining noise there is a brief second or two of a light popping sound.

My best guess is that it is something to do with the noise cancelling function, but I'm by no means any expert!

Has anyone else had the same problem?