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Thread: 1998 E36 323is - Head Unit Radio Alternator Whine - Can't Get Rid of It

  1. #1
    Join Date
    May 2015
    Location
    North carolina
    Posts
    11
    My Cars
    1998 BMW 323is

    1998 E36 323is - Head Unit Radio Alternator Whine - Can't Get Rid of It

    Hi. I have a 1998 323is. The previous owner put in a cheapo Dual replacement head unit. There has always been alternator whine coming through the speakers when the head unit is powered on. The noise varies with RPMs. There does not seem to be a separate amplifier. The noise comes through no matter what the input.

    I have searched the forum for "noise" and read about 10 posts. Nothing seems to be the same. Usually the situation is there is a separate amp.

    If I charge my phone from 12v cigarette lighter while the phone is connected to the head unit via a male-male cable to play music, the sound increases.
    If I disconnect the power to the phone, the sound decreases to the level normally heard.

    Things I've tried to fix:
    The alternator has been replaced twice, still whining.
    I added ground loop power isolators similar to the following: https://www.amazon.com/Axxess-AX-ANR...power+isolator.
    I checked and cleaned the trunk ground.

    Should I just try another head unit?
    Are there more ground points I should check?

    TIA, Rob

  2. #2
    Join Date
    Nov 2002
    Location
    So.California
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    19,577
    My Cars
    1995 M3
    I had a problem with this many years ago.
    I solved it by making a filter, I think it was band pass or hp.You need a cap and a choke coil iirc.

    Not an EE and I've not screwed with electronics for a long, long time.
    Walk a mile in my shoes and you are a mile away in someone else's shoes.
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  3. #3
    Join Date
    Sep 2005
    Location
    Salem, MA
    Posts
    6,752
    My Cars
    03 zhp, 97 e36m3, 04 zhp
    Rob, the issue most likely lies with the grounding of the head unit. Try running an additional ground from the chassis of the HU to a separate, bare metal ground. Must be firmly secured as well.

  4. #4
    Join Date
    Dec 2017
    Location
    Houston
    Posts
    96
    My Cars
    1998 328i Sedan
    I know Dual is probably the cheapest off the shelf unit you can buy, I'd say just spend some money and get a decent unit if you want to quit wasting time for a low buck aftermarket radio.

    I have quite a bit of audio and electronics know-how, and it sounds like you've covered most of the bases. From what you're mentioning with the cell phone charger it sounds like the unit either has a defect or is poorly designed to reject noise coming in from the power. If you've tried a power isolator, also try disconnecting the aux power wire that goes to the dash lights in case the noise is coming in through that. As Mless said, also try checking the ground. Maybe run it directly to the battery if you have an extra wire just to test. Noise may get picked up by the chassis sometimes.
    1998 e36 328i Manual Sedan in Cosmos Black - Currently restoring

  5. #5
    Join Date
    Aug 2010
    Location
    Honolulu
    Posts
    5
    My Cars
    2011 328i
    I echo the "check the ground connections" sentiment. That type of whine is usually an indicator.

  6. #6
    Join Date
    May 2015
    Location
    North carolina
    Posts
    11
    My Cars
    1998 BMW 323is
    Quote Originally Posted by bluewater328i View Post
    I echo the "check the ground connections" sentiment. That type of whine is usually an indicator.
    Thanks! I will try grounding the head unit.

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