I have a 95 RRC with 135k on the ticker. I'm starting to hear a buzzing sound through the speakers that is in tune with the RPMs of the engine. I've heard in the past the ignition coil can cause this, so I replaced coil... still hear the noise. I don't hear the buzzing all the time but seems to be getting worse. It also seems to get louder when on turn on accesories like lights, fans, etc.

Could it be the alternator is going out? Or could it be my radio is dying? It is an aftermarket deck that was put it before I purchased the vehicle.

Thoughts?

Thanks!