Regardless, the woofer sucking in like that indicates DC at the amp output, which can do harm to the speaker. It seems that only one channel of the amp is affected, which can happen. If you can unbolt the amp from the speaker and see if you can measure DC at the output terminals with it powered up, that would confirm that the amp is bad.
Perhaps you could send only the amp module back for service rather than sending the complete speaker... I would contact the company to see what they advise. Good luck.
Perhaps you could send only the amp module back for service rather than sending the complete speaker... I would contact the company to see what they advise. Good luck.