Originally Posted by jester156
sounds like you are picking up some interference from your alternator. I have had this happen in the past.
The cause is usually when you run your RCA (from HU) in the same path as the power from the battery to your amp. Try running them on separate sides of the cab, this solved my problems in the past.
I always run the sub power on 1 side, and all my signal feeds on the other.
the thump does sound like a ground issue or loose connection somewhere.
This is not true. Physics does not stop working in a vehicle.
It is a common misconception that noise from the alternator is picked up through the RCA cables. As long as there is some modicum of shielding and insulation, it is not going to happen. If you move the RCAs and the noise goes away, there was another issue at hand that was fixed during the process. The power wire is not the cause.
Alternator whine is most typically caused by a weak ground. This can be the ground for the amps or it could be the ground for the HU itself. Make sure that where you are grounding your amps is clean, bear metal and that the copper is securely attached. As for the HU, I will typically not use the ground wire from the harness. I will ground to a spot on the fire wall or to a solid point of the chasis near by.
That being said, I do typically run power and the patch cable on opposite sides of the vehicle because they are easier to conceal.