Mine does this too! I've tried a lot of troubleshooting fixes, but nothing seems to work. So far the techs at Verizon have 'narrowed it down' to being something that happens when I am plugged into the computer, but I don't think this is entirely the case. Here are the times that it has or has not opened the droid music player on me:
We started out plugged into the computer, with headphones attached.
The media player would start when using other apps, especially pandora, lastfm, games, or texts.
Recieving a text message would open the music player.
Clearing the phone's cache did not clear up the problem.
Deleting all my mp3s just made the music player attempt to 'play' a photo I had taken earlier that day.
We removed the usb charger, and the memory card, and after rebooting, plugged into the computer and sent a text. The text triggered an error saying that no memory card was attached.
So we unplugged the USB. This time, it looked like it stopped. I thanked the tech and hung up.
...five minutes later, I reinstall pandora, which soon starts crashing and spazzing, so I get an app killer and knock out the music player. It stops the music from playing but pandora is still dying. I uninstall it. Reboot.
The music player opens, first thing. I should note, all this time, my headphones have been plugged in.
I kill the app, unplug the headphones, reboot, reinstall pandora, and play it on the speakers.
No freezes, it has been playing steadily, texts do not prompt the music player, and even the phone going into sleep mode does not freak my phone out.
I am very inclined to believe that jamo is onto something with the headphone jack, but I just don't know yet. I'll keep updating as things happen.
Not cool, Droid. Not cool.
Incidentally, I have dropped my phone a very short distance about a week ago. Has a small ding from hitting the pavement but I thought it was otherwise fine. Are these things
that fragile? I hope not.