I was having some .... noise when the trim was going up and down he he he... anyway, Al and Eds in Ontario set me up with some PAC's RCA Ground loop isolators... solved that and many other issues.... They are directional when inline with the rca cables.
Worked for me...
Once again...a band-aid for bad wiring. If you run the wires correctly, you should not have a ground loop. Of course, most shops will not tell you that, since it involves extra work.
Try disconnecting the isolator and make sure your bass notes don't change...