Audio sounds compressed, hollow, and tinny coming out of my computer

Hi everyone -

I'm having an audio issue when playing files in iTunes 8.1.1 (10) and Quicktime Pro 7.6 (472) . I'm using ia Dual 2.7 Ghz PowerPC G5 running OS X Version 10.4.11.

Recently I discovered that all of my audio files (music and spoken word podcasts) started sounding compressed, hollow, and tinny, both when I'm playing the files out of my speakers (Harman Kardon Soundsticks) or headphones (Sony MDR-7606).

At first I posted this message over on the iTunes forum, but after playing the files in Quicktime I discovered that they still sounded compressed. The majority of my audio files are ripped from my CD collection using 256 kbps, 44.100 kHz, VBR, optimized for Velocity Engine.

I don't think it's an issue with the files themselves - they sound normal when I play them using the same version of iTunes or Quicktime on my MacBook Pro running OS X 10.5.6, which makes me think it's a software issue with OS X, or perhaps a hardware issue - but I'm totally at a loss as to what would cause this change in audio quality.

Does anyone have any ideas?

Thanks,

Dan