328i Buzzing from subwoofer.

I have a problem. Installed aftermarket amp and subwooders in the trunk of my 328i and have a buzzing sound comeing from driver side subwoofer. This also comes out of the aftermarket subwoofer unless i set the bass to zero on my head unit. I'm thinking interference somewhere in the lines.

Sub lines where taped with t-taps.



Any help would be great thanks.