Yeah that is rough. I have been though this a few times. It has always come down to upstream equipment for me (preamps mostly). But is sounds like your speaker may be the problem.
I would switch location (right for left) of them and retest just to make sure you are not getting room gain. But the frequency seems to high to be room gain unless the louder speaker is very close to a wall etc.
I would switch location (right for left) of them and retest just to make sure you are not getting room gain. But the frequency seems to high to be room gain unless the louder speaker is very close to a wall etc.