Leon R - Speaker interference

[LCR12npt]

I have just installed 2 alpine amps, infinity components front and rear and a JL Audio W3 v2 sub. The install has turned out really well and sounds great but at low volume with the engine running I am getting alot of interference.
The preouts are 4v, RCA's tripple shielded so cant understand why. I havent run a seperate battery power supply for the head unit, would this make a difference? Any ideas on the cause would be greatly appreciated. please help.

 

[D3DNA]

To me it sounds like a grounding problem. Check to see if your ground cable is connected to a good earthing point.

 

[lcjay]

other than the earth,could be you need to fit a capacitor,had that problem on a golf i had years ago mate