Vibrating noise coming out of Fender Hotrod deluxe III and for the life of me can’t figure out the cause

Whenever a really bassy note is played and especially if the note is an A, there is this rattling that comes from the amp that sounds like something loose vibrating. I tried checking the tubes, took off the backplate and find the vibrating bit, but for the life of me I cannot figure out where tf it is coming from. Sounds like it could be by where the on off switch is, but when touching the components to try and stop diagnose, I cannot find anything. If anyone has any advice here would greatly appreciate. Thank you