ok so i installed an aftermarket deck into my 1992 lexus sc300 and im getting a hmmmmm sound throughout the speakers and when i start my car the sound gets louder as my RPMS go higher ,


i wired the ground to the original ground ..... do i have to ground the "signal ground" as well ?

 

System ground

 

You have a bad ground. Run a dedicated 12V power and ground from the battery and that should fix your problem.

 

Or ground to a solid piece of metal and yes ground both that and the signal ground.....if that doesnt fix it. take the radio out and connect the ground to battery's ground and the power and acc to the battery's positive (doing all of this, outside the car) take a speaker output to a junk speaker or something like a home speaker. have a buddy his the gas and see if the problem remains if so, replace or fix the broken ground connection inside the brain of the radio

gl