Greetings all,
I do not have a QMX, but upon reading that the problem went away when the audio output was connected to a line-level input AND that it seems to be volume-related, the sound engineer in me saw a couple of flags. First, ear buds are usually in the 32-ohm and less range while headphones, while varying wildly, can range up to 150-ohms (maybe higher). For reference, my Sony MDR-7506s are spec'ed at 63-ohms. That said, a line-level input is usually going to have a load of at least 1.5k-ohms, so you're loading down the audio output amplifiers significantly more when you plug into a line-level input. Second, since people are reporting that it gets worse as the volume is increased, perhaps what's happening is simply the audio output amplifiers are clipping and/or there is clipping (either analog or digital) elsewhere.
My $0.02 :-)
Charles Johnson
KF4AYT
