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They could Write a book on how to get rid of motor noise!
Start with how the wires are Routed.
1) Never run the Audio and Power Wires together.

2) Always use the Body of the Car as the Ground not a Direct Wire to the Negitive post of the Battery.

3) Replace the Capacitors on the Alternator.

4) Look for loose grounds on all components.

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I have the rca running down one side of the car and the power 0agu and remote cable down the other side, the head unit is grounded to the chassie not using the orig ground cable, the amps are both ground in the same place next to eachother with 4agu cable, the noise comes without the headunit turned on and its a whistling noise, also i can hear the changing when i indicate, (louder, quieter) ive tried changing the gains and it worked but the audio was almost off, no speaker / audio cable is near the power cables, not sure if its the spark plugs/ alternator/ or distro cap, ive changed the ht leads and its still noisey.
Any suggestions, i have a turbo pac 1 line driver on, what was inducing alot of the noise but as its only small amperage i put a suppressor on that and that cured that. but when i unplug that from the amps its still there, what leads me to beleive i need a suppressor on the main power from the battery, whats the changing of the caps on the alternator, can you divulge more on that one?
thanks

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Hotwaterwizard,
Isn't it best to use a Star Configuration that has separate power and ground wires in order to avoid loops?
For example, the car uses its chassis as the ground for rear turn-signal lights. If the amp used the chassis back there as its ground, then its supply ground voltage will fluctuate with the lights, due to the voltage-drop along the chassis. Since the head-unit is grounded up-front, then the amp's signal input voltage will also fluctuate with the lights, having a voltage divider that is the shield of the signal cables and the chassis.
Connect the amp and head-unit power and ground wires directly and only to the battery.

Stuee,
The whistling noise that you hear is called alternator-whine, and its volume varies with load, as you hear when indicating (turn-signals).
A small amount of alternator ripple is normal, and car sound equipment have filters that can usually cope.
In your case, the head-unit is grounded to the chassis, and so is the alternator. But your amps are probably grounded to the battery (you din't say where), so the wire between the chassis and the battery has a voltage drop that is in series with the amps' input signals.
Remove your head-unit's chassis ground and ground it at the battery instead.

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Stuee,
I believe that you have a ground-loop problem that is caused by your components being grounded at different locations. It doesn't matter that the head unit is turned off, it is still grounded.
To prove the ground problem, unplug the RCA cables at the amps. If the noise is gone then the problem is that you have 2 grounds instead of 1, as I explained earlier.
Instead of running heavy ground wires from the amps to the battery, disconnect the head-unit from its ground up-front and connect it to a suitable wire that runs to the amps ground point.

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The amps nor hear unit run ground to the battery that are grounded to the chassie, i put a new 4agu ground cable from the battery to the chassie at the front of the car as was told would improve it, but never worked, so nothing is grounded direct to the battery, jsut throught the chassie.
Thanks for the help so far.

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Stuee,

Audio guru has a good point about the voltage differential between the 2 ground points, although I don't recommend that you ground anything directly to the battery, that's what the chassie is for. You should really consider moving your head unit ground to the same location as the amp ground.

Are there any other components in your system? Active crossovers? Power capacitors? Cold cathode lights? They can induce noise into your system also.

Maybe redo your ground points. A dremel tool is great for exposing sheetmetal.

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I have Been an Audio Tech for 25 years. In my opinion You can not find a wire that is Big enough to replace the Body of the Car.
The best possible Ground is the Car Body.
Another Hint to Moror noise is to put a Large Ground strap from the Hood to the Frame. The Hood is not Usually Grounded and motor noise escapes from the hood area.

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