I'm having some strange issues on my MBP Retina running OS X 10.8.2.
The audio balance changes, and the right speaker is almost muted.
Anyone know what could be wrong here?
I've had this problem on multiple MacBooks (from my old Powerbook 15 from 2003 to prior to finding this question on my late 2011 MBP 13").
Apple has acknowledged it as a bug when pressing the volume buttons during heavy CPU usage way back in OS 10.2! The solution was to go back to preferences and set it back where you wanted.
I have this exact same issue. mid-'12 rMBP 15'' 256/2.6/16GB. OS X 10.8.2
First noticed the sound issue with my ear monitors (Shure headphones) plugged into the computer: the sound in my R earbud was like 80% diminished. But the earbuds worked fine on my iPhone 5, perfect output in each side. Last night, while watching a Netflix movie (occasionally plugging in my earphones into the rMBP), the laptop's R speaker suddenly lost all output. I freaked out, obviously, but quickly discovered that the balance bar had been shifted 90% to the L. Funny how that just changed itself mid-movie watching. Also, after I fixed the slider bar and the laptop's speakers started functioning as normal, when I plugged my earbuds back in, I had to go BACK into Audio preferences again to change the balance bar. Strangely enough, it was shifted L again, but more like 50%, not as extreme as it was for the laptop's speakers themselves.
Absolutely a software bug.