Review on Enhanced Noise Filter B25N: BOSS Audio Systems Ground Loop Isolator for Optimal Car Audio Performance by Chris Pacino

Fits me perfectly. I have a Cadillac STS with an aux connection via RCA under the armrest. I wanted bluetooth so I bought a car bluetooth adapter which I plugged into cigarette lighter cables that plugged into the RCA ports. The bluetooth adapter worked great until I started the engine, I had a strong hum from the alternator that got louder as the engine revs and a loud hum that sounded like an airplane. I ordered this adapter along with a BOSS B15N squelch that plugs into the power cords. The B15N didn't do anything, but this B25N worked like magic, completely removing both unbearable noises and now the audio is totally silent. I was concerned about the loss of quality, some people seem to think this adapter removed the frequencies that made the sound poor and/or weaker, but that wasn't the case for me, crisp, clear sound. It seems that many users who have problems with sound quality use this device for subwoofers.