What's the easiest way to tell if the two subwoofers under the seats are working as they should? I tried playing some bass sounds, but I couldn't see the subwoofer moving at all. I have the bass setting on 9 from the beginning, but I never felt any bass under me and can only feel the bass from the door woofers. It's been the same since I got the car, by the way. So I'm just trying to know if they're working or not. My Stinger is the GT-Line with the Harman Kardon sound system.