Take a good look at the cones,if the foam edges are cracked that would explain the sound. Also, I have found my 14 year old MTX box will not produce bass if it's really cold (below 30 degrees) until the car warms up..The cones suspension gets stiff. Make sure both woofers are actually working, maybe one is blown or rubbing the voice coil, and all wiring is good. I imagine you crank the tunes a bit more than me.
