That Alpine 3544 wasn't made to run 2ohms in bridged mono mode. The amps output is clipping therefore distorting the output to the woofer. Eventually you can blow the woofer.
If the woofer is moving and no sound is being played from it, this means the amp doesn't have a high enough damping factor.
It doesn't have the ablility to control the woofer's movement accurately. This could be caused by wiring the woofer's voice coils in parallel making the amp see a 2 ohm load.