you should try to mount it somewhere other than on your box. the vibration from the bass could break something in the amp. if you dont have room to put it anywhere else you should put something underneath it. like another layer of 3/4-1" MDF. and maybe piece of rubber.
wat happens its that sometimes some components in the amp are not soldered correctly so when it bumps or vibrate it will start to rattle and some components will get off contact with the circuit board... but that happens one in a million...