This just totally baffles me.
I have been involved in VoIP forums for a while now and have never heard of such a phenomenon. I suspect someone's getting a good laugh out of this.
I re-booted my router and PAP2. That seems to have fixed the problem. I made a couple of test calls and the music is no longer there. That still leaves the mystery of what caused the phenomenon in the first place...
Will the culprit please come forward!