Try the out convertor/factory amp interface. This installs in the line between the radio wiring harness. since the radio is aftermarket I assume you had to put a harness convertor in it. You will have to recut the wires and install this unit inbetween. The convertor has gain controls built in which ...

Need a little help I installed the Panasonic CQ-CB8901U HD radio and get a low hiss in the speakers. It's happens whether the car is running or in Acc position, AM/FM/CD. does not change in volume when I accelerate or when I increase volume of the unit. I turn the volume down then it's more apparent...