Crushed Voice Coil

OMG, turn off that bass boost, turn the bass control on the deck to it's center setting. There is a very good chance that you are running the amp out of power, I see that this amp gives up to 18db of boost @ 45 hz. This much energy put into the speakers at higher volume levels will most certainly cause a loss of control of the motion of the driver, thus there is a very good chance that the voice coil former is actually striking the magnet or pole piece. I have not had much experience with the Cadence subs, I have them available to me if I want, I have gone with what I feel is a better product for my customers. This all points to the amp being driven into clipping, much like driving your car above redline on a permanent basis.

I spoke with him last night and the radio does not have a bass boost.  The only option on the radio is the line level output adjust for the subs.  He does not have the line live but half way.

The bass boost on the amp is not turned up either.