Beats Fit Pro one side lacks bass

There is a big difference in bass between my left and right Beats Fit Pro earbuds. Both sides pass the Fit Test and pressing on the right one does not change its lack of bass. This happens when connected to my iMac or my iPhone and is most pronounced when I put balance all the way left, then right to compare. I have reset the earbuds twice with no difference and tried various audio settings. Any suggestions, other than returning them?