Retina MacBook Pro - balance getting out of whack?

Is there some keyboard shortcut to adjust the speaker balance that I'm accidentally setting off? Every now and then I'll be listening to music and notice it sounds a little strong in one ear (usually the left) and then I'll go into System Preferences > Sound > Output > Balance and notice that it has been shifted slightly to the left, despite me not actively doing anything.

I hate it especially because I've had hearing issues in my right ear before and I keep thinking something's amiss with me, but I realize it's my laptop. Why is this happening? It's happened with both iTunes and Spotify, so it can't be an issue with a specific program...

 

It's weird...this was a constant issue for me on my old Powerbook G4 running OSX Tiger. Never figured out what was causing it, but I remember it was a constant issue because music where different instruments were played through the left and right channels got totally messed up.

Probably not helpful to you, but this definitely rang a bell for me.

 

It's an odd problem, isn't it? I wonder if it happens when I keep switching between headphones and the on-board speakers...