I have an 02 with factory speakers and radio, no dsp. I have noticed lately that when listening to bassy music, I have 1 or 2 subs that will make a gurggling sound. I have narrowed it especially to my passenger door. Sometimes the bass will hit, and then the next second, it sounds like it is popping or hitting something, the gurggling sound again. I had my dealership look at it, and they could not duplicate the problem. Any suggestions? Thanks.