I have 13" MacBook Pro (Late 2009) model that is refusing to play sound on the right audio-channel.
Without any speakers connected it still plays fine but once I connect earbuds or a headphone, I only have sound in my left ear. In my right ear I hear a very low white noise sound.
I've tried rebooting, fixing disk permissions (very long shot, I know), same problem if I play sound in a virtual windows machine. And off course I've verified that the sound balance is set to both left and right.
I've "looked" into the mini-jack output but can't see anything wrong with it…
Best Answer
It is probably some dirt in- or another problem with your sound-output jack.
If twisting your headphone-cable or repeatedly plugging it in and out of your MacBook does not work, you might fix it by doing something like (gently!) poking into it with the backside of a matchstick or trying to clean it with some cotton buds. In that case make sure you have one that does not fall apart easily or you'll end up with a cotton-filled connector.
If that does not work, I'm not sure if you are able to fix it yourself since your MB might need to be taken apart to get into the jack and clean it…