Oh another thing to check is if you use audyssey or not with your receiver. If so check to make sure it didn't do anything dreadful like set the individual trim extremely high on that speaker. You can try disabling any auto EQ as well. I doubt this is the source of the problem but worth checking anyways. If you didn't use any auto calibration just ignore this troubleshooting step.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne