seriously, I learned from my teacher that a bass amp 'connects' or resonates with the floor. Majority of the time it is a good thing. I learned on TB that some amps resonate in a bad way. I play at a jam & use the house bass amp but resonates in a bad way with the floor. I would have to turn the bass tone down for it to quit the 'rumble sound. Someone on TB mentioned tilting the amp back to help this. So I raised the front of the amp a few inches & resolved the issue.
