Foobar2000 also has the ability to test MP3 and other audio types for sync errors.
Correct me if I'm wrong, but... I thought sync errors only caused audible "blips" occasionally in the music stream (because a sync error is a missing header on a "frame" of audio data in the MP3, and when the decoder encounters a headerless frame, it skips it, causing an audible blip). I wouldn't think this could cause the mixing that the parent poster is talking about (and which I've heard).
I'd strongly suggest you do a thorough scan of your hard disk with the utility provided by the manufacturer of your hard drive (use the "long" scan option if it gives you one).
If it finds a number of bad sectors, I would be hesitant to rely on the drive further, even if the tool reports it can repair them. The truth is that there
is no way to repair a bad sector, it simply marks that the sector is bad and the drive doesn't use it anymore. All drives have some bad sectors, but they shouldn't show up in these tests because they should be hidden by the drive's automatic internal defect management (they are scanned after they are first made and the defects are mapped and the drive never uses them). However, as drives age, they commonly "grow" new bad sectors as they begin to fail. This isn't so good.
If you only find a handful (5 or 10 or 20) and the drive is a little old, this might be okay, but I'd begin to "not trust" the drive and only use it for non-essential data. If the scan finds hundreds or thousands of bad sectors, then it's not just growing them, but it has full-blown defect cancer and it is time to lay the guy to rest.
Some good free tester tools are listed here:
http://pcsupport.about.com/od/toolsofthetrade/tp/tophddiag.htmThe best tool is really SpinRite from Steve Gibson. It isn't cheap, but it is the best. More info here:
http://www.grc.com/sranalysis.htm