Leaving work last night, I noticed a radio hum. I have an aftermarket Alpine. It makes the noise as soon as you turn the headlight switch to the parking lights, and stays if you keep going turning on the headlights.

It's a constant level/frequency, so I know its not engine/ignition noise, and only happens with parking/headlights.

Should I start with the vehicle wiring or the radio's wiring?? Related or not, I dont know, but is it normal to hear a relay click from the glovebox/passenger footwell area when the headlights are turned on?

Thanks for any insight., The hum is not too loud. If I turn the volume up to (my) normal listening level, I cant hear it. Only when the volume is down real low can it be heard.

 

generally speaking noise is introduced into an audio system by grounds, what it sounds like to me is the parking light switch and the radio are sharing the same ground and it is becoming weak. My first step in fixing this problem would be to run a new ground to the radio, I would use my wire brush to scratch the paint off of the truck somewhere relatively close to the radio then use a self tapping screw and a ring terminal to make the grounding point. If that does not resolve your problem let me know and I will suggest another step.

 

Will do with the ground. If i remember right, I think there was a noise filter in-line with the positive supply to the radio, going bad?

 

Well, I ran a new ground. No more noise. But now the paranoid side of me wonders how long the previous ground will work for the headlight switch. Thinking maybe I should re-do it before it becomes a problem.

 

there are factory grounding points in each kick panel that provide for most of the dash, never hurts to clean them if you are noticing any fluctuations anywhere.