I use my N2 while cycling. I have never had any issue using Google Play music. The last time I went cycling, this exact same thing kept happening. I would be listening to music, and the volume would start dropping and eventually go to zero. I could unlock the screen, move the volume up by hand, only to see it shoot right back down to zero. This is the most annoying thing I have ever run across. I am begging to think that the software monitors how long you have had the headphones at a high volume, and just shuts it down.
I cant think of anything more annoying while trying to ride a bicycle.
It just started doing this recently, I wonder if there was an update of some nature to make this happen.