Car Stereo - For Swift!?

That "bur" sound is probably coming from your speakers. Try to turn the b down on your head-unit for the speakers. That should let the subs take care of the b. I don't know what subwoofer box you have, but the one for real punchy b is the sealed box. Ported and bandp boxes are real boomy. Hope this helps, e-mail me if you need help!