Why is my sub turning on and off?

no the screw in the back probably got loose from all the shaking...just go to the back and make sure all the cords are on tightly...if that doesn't help, it's most likely the amplifier - nothing serious, sometimes the cord connection inside the amp gets broken from all the vibrations too, if it's a cheaply made amp or just been used a long time...you can fix it yourself with a souldering iron