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having an issue here with a full audio system.

Car: 2009 Subaru Impreza 2.5i hatchback, manual System: Front Speakers: JL C2-650 components Rear Speakers: JL C2-650x coaxials Sub: JL 12w03 Amp: Alpine PDX-V9

I'm having an issue with noise. Specifically, supercharger-like whine(that changes with RPM and also gets louder when I crank the fan) coming from the front tweeters. It is not an issue with power(unplug the RCA's and it goes away). It is seemingly not an issue with the RCA's either as when I unplug the front component speakers, the rear coaxials do not whine. However, if I plug the rear RCA's into the front speaker inputs on the amp and vice versa, the front still whines but the rear does not. Also, the noise remains even with the RCA's running completely oustide of the car. I have a suspicion that my speaker wire going from the crossover to the tweeters may be picking up the noise but I'm not sure. That wire is NVX speaker wire but it's not even remotely close to the power wire. If you have any ideas what could possibly be making this noise and some remedies please lend a few words of wisdom as I've been fighting with this thing for a year to no avail. *Note, the head unit is already grounded to chassis. Didn't do a thing. Thanks!

EDIT: I have already tried an in-line noise filter on the power cables and a ground loop isolator on the RCA's to no avail. Talked to an audio pro and he advised me that since the whining went away after I unplugged the RCA's, the noise was somewhere at the RCA cables or head unit. But, if this would be the case, wouldn't I have noise in the rear speakers too? I'm befuddled.

EDIT #2: so I took it to an audio pro. We've come to the conclusion that it is not coming AT ALL from the power wires (goes away when RCA's are disconnected) and it is not coming from the RCA cables as the whining is in the front, no matter the configuration of the RCA's to the amp(even though it goes away when we disconnect the front cables). Power line noise filters didn't work, ground loop isolators didn't work, no RCA noise(even with the cable running OUTSIDE the car it still whines the same). Only thing I can think of left: either the head unit is picking up noise(but I'm not sure because the rear crossover speakers don't whine) or the inductors (coils of magnet wire-basically an electromagnet) in the front speaker crossovers are picking up the interference. I'm going to try and Faraday cage the crossovers with aluminum foil and ground it to see what happens.

EDIT(again): so turns out there IS whining coming from the back. Eliminated grounding issues, but noticed the resistance between the RCA shields and the head unit ground is 3 Ohms. Higher than it should be, but if I run a wire from the shields to the ground it doesn't get rid of the whining. One concern I have, however, is the length of my amp's ground cable. Does anyone know if a too long ground cable can cause noise(it's going straight to the battery)?

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    Just a thought: If you're getting interference / EMI on the wires going to the speakers, and your filter is too far away from the speakers, the filter won't work very well.
    – 3Dave
    Commented Jul 6, 2017 at 14:31

2 Answers 2

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This has less to do with the audio signal, than it does with grounding. What you have described is a ground loop.

You likely have a grounding issue somewhere. Obviously we are not able to tell you where that is, so you will have to do some troubleshooting.

Here is a great article on how to troubleshoot car audio noise. Here is another on Diagnosing and treating noise problems in your car audio system.

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  • Thank you for the advice. However, I have tried both power source noise filters and ground loop isolators and neither work. However, I also might have some no-goes install. First, I grounded the amp directly to the battery. Second, I(just yesterday) grounded the head unit to the firewall so there would be a ground loop. I'll try moving the ground power cable to the firewall too and see what happens?
    – spencerktm30
    Commented Jul 6, 2017 at 11:59
  • Sounds like a plan.
    – Lawyer Aidroos
    Commented Jul 6, 2017 at 13:17
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Ladies and gentlemen, I have found the solution. CharlieRB definitely called this one. Thanks to him! Turns out the issue I was having was because I grounded my amp to the battery, not the chassis. Moved it to a chassis ground(same as where I grounded my head unit) and the whining went away!

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