I have the quiet comfort over ear noise canceling headphones. Just a few weeks ago, I noticed static on the left ear. Plugged into the PC, plugged into my phone, didn't matter, static on the left. Remove earphone cable, still static on the left. Turn off the noise cancelling button, static stops. Replaced battery, static on left side still there. As others have indicated solution is easy Remove the ear cup, Remove the felt piece, I noticed mine had moved, and wasn't in its proper place. I then blew on the mechanism a bunch of times, reset the felt to its proper position, and whamo, no more noise. You could also try the knife method to increase the space which you can clearly see has only one way to do it. But this isn't a Bose problem, this is a long term use problem. Just clean it people, and whamo, you have working headphones again.