First thing to try is resetting your fcp preferences
It's also possible your sequence has gotten corrupted. Try editing a short clip into a new sequence and see if that works.
And what are your sequence settings?
Also, although its a long shot, make sure the frame rate of your easy setup matches the frame rate of your sequence.
Thanks for the suggestions. I tried everything listed, but it's still not working.
I just ended up exporting the clip I needed to fix out of FCP as an .aiff, fixing it in Soundtrack Pro then exporting back out, and brining the new clip into FCP and laying it over the old. It's not ideal, but hey, it works! Haha!