wooferman

You can rule polarity reversal out. Polarity reversal's only detramental effect is if it is cancelling out the sound wave of a neighboring speaker (for the most part). An amplifier can malfunction and not correctly push a woofer. I had this happen from a Kenwood amp once. One other thing is if a subwoofer surround is torn it can force a speakers cone outward (sealed box only)... seen that happen, so inward is a possibility. Troubleshoot how you can one component at a time. You may be able to pinpoint the culprit, but if your head unit had a malfunction you may want to start there. Hope all goes well!