I am getting a high humming sound coming through my speakers if the amp is on but no radio. Amp is grounded good and is powered though a dist block going direct to the radio with good quality 4 gauge wire. Obvoiusly this is coming through the alternator or whatever. I know there are noise filters I could get but have not ever messed with them, can anyone recommend something to try and where do you put them, like in line with the power wire going to the dist block or before the dist block??