Your vehicle's active noise cancellation system (ANC) plays havoc with an aftermarket system's output — with bass tones building up and then disappearing, over and over again. Whether you knew about this issue before you got your amp or sub, or found out the hard way, you need to disable the ANC in your vehicle in order to get good sound. iDatalink's bCH3 ANC bypass harness plugs into the factory wiring as a jumper that bypasses the noise cancellation module, allowing your new system to play the way it should.