OS X :: MBP Speakers Sound Bad?

My internal speakers sound broken, but according to Genius Bar it is apparently a software issue and they recommend an OS reinstall. I am hoping to hear some alternative suggestions. A few days ago while playing iTunes, my MBP (unibody, late 2008 and in use since December 2008) began sounding bad. It sounded as if the internal speakers had blown. Not all songs produce ugly sounds, but within a certain sound range even classical piano music and relatively quiet songs with strong vocals now tend to become unclean ounding/reverberate.The Genius Bar employee rans some tests and concluded it probably is due to some kind of corruption of software, and he advised me to reinstall Mac OS.He tested

1) if the mp3 file was damaged. Negative, a copy of it sounded fine on another MBP.
2) if the sound was bad when listening to my MBP with headphones. Negative, sounded fine on the headset.
3) if my MBP would sound bad when booted from another hard drive that played the same sound file. Negative, my MBP speakers now played that song just fine.

He also used disk utility and found no hard disk issues. He ran another test with disk utility, looking at a long list (that I don't know what is) but could not see any particular problem there, it seems. I have subsequently tried to reinstall iTunes, but that has not helped, and am now hoping for a suggestion other than an OS install which I imagine can cause a lot of trouble (not so much the installation as such, but more the subsequent tweaking of various applications that I have had a great deal of trouble setting up).