Are there a bunch of effects loaded into any of the tracks or onto any of the buses?
You could test out the potential interference of any such plugin quite simply: just prior to hitting Play, first hit the letter 'E' on your computer keyboard. This will toggle the 'Bypass All Effects' function in Sonar, so if any plugins were causing problems bypassing them and then hitting Play should clean up the sound (though you wouldn't hear the effects).
SOOOO, if you DO run through listening after bypassing effects, what happens? Is it better? If so, then one or more of your plugins is likely not meant to be used during recording/tracking, but is instead meant for mixing/mastering.
Can you please perform the above test and post back the results? (also, after running the test, hitting 'E' again will toggle the effects processing back on).
Thanks,
Bob Bone