jaytor OP
Strong bass causing buzzing behind the wall
Find where it’s rattling by placing your hand on the drywall playing the music that sets it off.
This will be the spot where you have to fill the square inside made up of the "studs" and "noggins" see link
The distance between the "studs" are around 20" and the distance between the "noggins" around 18" or the other way round.
This is the square you have to fill with the expanding foam, make a hole in the drywall to put the nozzle in and squirt the foam up and down inside in for about 6-8secs only, should be enough, then fix or hang something over the hole.
https://www.carpentry-tips-and-tricks.com/images/460x460xStudwork.jpg.pagespeed.ic.L5OnQuYSr3.jpg
Cheers George