alternator whine
 

I'm getting this annoying alternator whine through the speakers after my install.

I just installed these in a 2006 BMW X5 Base stereo...

Sony MEX-BT3900U
Phoenix Gold RSD 6.5" Components
MB Quart REF4.50
Raptor ISPKBL4 4CH Amp install kit with RCA's

RCA's are wired through the driver side door sills and up the dash.
Power is at the +batt post. Ground is at the main bolt where the neg battery cable is grounded to.

What I did to troubleshoot was connect only the amp and the L/F speaker. I disconnected all the wires from the headunit. If I plug in just one of the routed RCA cable to the amp I would get alternator whine. Disconnect it. The noise goes away. Plug in a muted RCA plug that I made. No noise. Plug in a regular 3ft RCA. No noise.

So did I narrow it down to induced noise in the RCA cables or is it a bad amp ground? Thanks for the help guys.

Alernator whine is almost always caused by a difference in ground between the head unit and amp. So, double-check the quality of the amp ground. If that is good, and you still have whine, consider running a new ground line to the radio from the same point.

Next, confirm that the ground wires of the audio out from the HU are connected. On some BMWs, the audio ground wires were cut and tied back at the radio.