Issue with Logic 7 Subwoofer - Buzzing/Grumbling

Today, on my e92 2008 335i coupe with Logic 7 sound package, I am having an issue with my subwoofer under the passenger (right) seat. It seems to be vibrating/buzzing/grumbling, in an unnatural way. See youtube video I just uploaded below.

It starts occurring, not for from all bass music, but only once the bass gets very strong in the song/or if on high bass setting, then it stays on with ALL the bass (even quite bass) until the car is shut off for more than 10 minutes.

Could this be due to the subwoofer failing? wiring problems? problem with amp? something else?

If so would this be covered under my BMW CPO as the original warranty has expired (only ~40k miles, but it has been more than 4 years as of 3 months ago) ?

Thank you for any help.

Youtube video link of the sound: _a_