Trunk Opening Automatically!

Yesterday, I pressed the door unlock button on my fob, and the trunk opened along with the doors!  Confirming I wasn't a) crazy, and b) hitting the trunk release (which wouldn't make sense because it's a "hold" button), I closed the trunk and tried it again.  Sure enough, it opened again.  Then last night, it actually opened WHILE I was driving (no button pressed).
 
Any guesses at a cause or how I can diagnose it?
 
Thanks in advance.

I should mention this is a 1999 Jetta IV GL.

Do you happen to have a system in your trunk?!?!  I had a similar problem at one point in time ... my system was actually hitting so hard that it would pop my trunk and it eventually busted the truck latch!   However I did have 4 12s in the trunk so yea. 

hehe that must have pumped! ok. umm. have ur keyless entry system checked. you dont by any chance have a rogers phone that you were on all of those times? because my rogers phone sqrews up all sorts of electronics. moniter, radio, tv......