It's kind of a tough one to explain - as I can't work out why it's happening.
Basically at times while I'm listening to music I'll notice it doesn't seem as loud in one ear (using headphones in the only comp jack) and I'll go to the advanced volume properties and the balance of the Wave bit will have moved (always to the same place) as shown in the image below.
It seems to only happen sometimes when a new song starts, but if doesn't happen every time the song changes and I can't really tell what's making it happen.
Any help with getting it to stay in the middle would be much appreciated, cheers.