Now that I'm at home I can check those settings...

In MMJB go to the menu 'Options' and choose 'Settings'. Click the 'Recorder' tab. For good quality MMJB encoding check 'Custom Quality' and move the slider to 192 Kbs (at least). Click the 'Advanced' button. At the bottom of this dialog box there's a 'Maximum Bandwitdth' Section. Uncheck 'Let Encoder Choose' and move the slider to 20 kHz. Then click 'Ok' then 'Ok'. Try re-ripping a song you find it particularly noticable on and see if that makes any difference (it should if it's an encoder issue).

As Tony said, it could be other things as well, such as your amps over-driving your speakers or some other issue. You just need to eliminate the MMJB encoder.

The above directions are for MMJB Plus, but the standard version should be the same (hopefully).

Hope this helps.

-Zeke