[Elecraft] K3 Mufflied audio - new issue

[Ham Radio]

I was operating tonight after some fun this weekend working some nice DX since conditions were so great. I decided for some reason to listen to my audio on my K3 serial 1391 and it sounded really muffled.  I switched to my other K3 and everything sounded perfect with same two headsets switching back and forth.  There seems to be something weird going on with 1391.  I am not sure if I should do a reset or if there is some other procedure I should run through.  Using the headsets on 1526 eliminates the possibility of a headset issue.

The audio sounds somewhat clear but with a muffled background noise which is difficult to describe.  Usually my audio is super crisp and clean (that is what people tell me).  Not sure what has transpired.  I was considering doing a reset but thought might be a little extreme.

Any help would be very much appreciated.

Thanks,

Keith
AG6AZ