Only other thing I could think of is switching the front and rears on the amp, and seeing if the problem follows the wiring or the ports on the amp. If it follows the ports, it's the amp at fault. If it follows the wiring, it's either the wiring, the speakers, or the acoustics to blame.
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#2529 [blue]Mk2a 10GB + Tuner[/blue] Original reg #3422 http://www.bitshift.org