Anyone wish they had a rumble subsonic filter?

A good rumble filter will attenuate differential signal, which is vertical groove modulation, without affecting horizontal modulation. If you have a single subwoofer (or two) driven in mono (mixed Left and Right) this will solve your problem. I bet you could Google "rumble filter" and find a diy kit.
By the way, the pumping of your woofer cones does affect the sound although you may be used to it and not notice.

I have KAB's rumble filter ($170) and it completely solved my problem. At first I didn't understand why my woofers were going nuts, then once I finally learned what the problem was, I was able to get a separate rumble filter and life is good.

Michael

Dear 240zracer: The Eldartford suggestion: run the subwoofer in mono way is really the best one because you don't have to add any other " stage " ( rumble filter ) to the signal.

Like Eldartford already posted the pumping in your woofer cones are adding intermodulation distortion and certainly makes a degradation to the signal reproduction.

Regards and enjoy the music.
Raul.