From time to time the audio on either side will drop with some static when I touch the jack. The problem seems to be persistent at this point so I'll have to open a ticket. A real shame too... All that waiting just to RMA it in weeks -_-
I've been using the M1 recently and the M1 is perfect honestly. As were the ATH-AD700 and FC700 when I tried them. I may have to open up my Klipsch Promedia IEMs just to quad-check but at this point the M4 seems to be to blame. Honestly though, when I first received the M4 I immediately thought the M1 had better build quality. At any rate hopefully this replacement won't take long, I really enjoy the sound signature of the M4, without a single EQ change.
It sounds like the jack, but it's strange that it doesn't have that problem with your other players. The M1's do sound good, no doubt, but I have to disagree about build quality in comparison. Don't get me wrong, the M1's are solid, but they're plastic, compared to aluminum on the M4's. Anyways, I hope you get the situation ironed out.