Car audio ground loop whine

For the last few months I have been trying to fix a whine coming through the car audio system when the engine is running. It came on all of a sudden, and only on the front speakers which are powered by separate amp and go through crossovers. The noise is present no matter what input chosen: tuner, CD, aux, USB.

What I have tried :

-redid all grounds, signal, and power leads to front speakers, crossovers, and amp
-ran new power and ground wires to head unit
-swapped in another amp
– tried alternate pair of rca jacked leads from head unit to amp, straight run, not crossing power lines
– new antenna and lead to head unit (old one was really bad at head unit)
– if I grounded amp directly to battery post instead of body, noise was louder. BTW, the amp ground wires are a short run twisted trio.
-pulled alternator brush pack and cleaned connections
-pulled the noise reducing capacitors on alternator and cleaned connections
-removed the diagnostic plug (TDC sensor lead and plug) from alternator
-pulled distributor cap and cleaned, above and below black plastic shield
-cleaned up edge of rotor
-cleaned all the grounding points (pivot bolt area etc) on alt. body

I did notice that the whine would disappear if the radio antenna was not connected. I talked to a few people and most told me to install a ground loop isolator on the low level lines from head unit to amp. Yesterday I talked to an ex-car audio installer and he advised to try grounding the RCA jack shields. That advice and the information here, convinced me to try it, and miracle of miracles, IT WORKED! Not a hint of noise or whine. To say I’m chuffed would be an understatement.

The head unit is a Pioneer DEH-P5000UB.

  1. #1 by David R. on April 18, 2011 - 8:46 am

    Interesting! I’ve never seen that before.

    • #2 by albell on April 18, 2011 - 9:38 am

      look at this diagram David B. sent to me. See how the 3 grounds (power, signal, chassis) are isolated by capacitors. But also note the comment about in some cases the cap(s) should be removed. Also some internet sources say that some Pioneer head units blow a tiny resistor that then produces this ground loop condition.

  2. #3 by Simon on April 25, 2011 - 8:59 pm


  3. #4 by jim on April 24, 2012 - 2:32 pm

    Tried running the power cables on the other side of the car?

    Power cables on left side and signal cables on right side?

    that made noise in my mate’s car, the noise gets higher when u put some more RPM on the motor

    • #5 by albell on April 24, 2012 - 5:22 pm

      I did run the signal cables as far away from power line as I could, max of a couple o feet. Did not solve problem. Grounding the RCA jacks did the trick.


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