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Sound coming from rear at around 40mph

Discussion in 'A3/S3 Forum (8L Chassis)' started by leshkin, Oct 26, 2010.

  1. leshkin
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    leshkin Speeding in reverse gear

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    Wondering if anyone had this or could know/guess what the problem is...

    When I drive at about 40mph, gets a bit louder after the car has warmed up a little, I always seem to get a quiet low frequency rumbling sound as soon as I come off the throttle and it stays there until I begin to accelerate or brake with some force. Slight changes in speed do not affect it much (pitch does not change). I have noticed this happening for a few months now and it does not seem to affect handling in any way.

    Ideas so far:
    1. tyre noise - slight reduction after switching rubber from a different car, but still there
    2. wheel spacer - haven't tried to remove this and check if the sound is gone (on my list of things to try)
    3. wheel bearing - jacked the car up and spun it, with no problems found
    4. CV joint - not sure about this as I never had a CV joint go on me yet and not sure of the type of noise this makes
    5. tracking out??? not sure about this as it's not pulling

    Anyone have other thoughts/ides that I can try?
    #1
  2. s3dave
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    s3dave TFSI Hybrid

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    Rear diff bearing..
    Drive shaft out of balance..
    tyre out of shape..
    Loose exhaust heat sheild (resonating)..
    #2
  3. BASS 666
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    BASS 666 BMW aye right dead on..

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    most times a wheel bearing will be noisy under load if you jack it up you prob wont hear it. is the noise on one side or central ?
    #3
  4. Jonesy
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    Jonesy Member

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    I've got a similar noise but its more like a whine coming from the rear. Been told by a Audi specialist that its the rear dif. I hoped changing the haldex oil and filter would fix it but it made no difference. You get the noise when you come off the throttle or when slowing down, goes away when you accelerate.
    #4
  5. BASS 666
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    BASS 666 BMW aye right dead on..

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    must admit it does sound like the dif..
    #5
  6. sean_s3
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    sean_s3 Member

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    The rear diff and the haldex are two seperate units , the rear diff is on my to do list when i have it serviced next.

    Cheers
    #6
  7. leshkin
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    leshkin Speeding in reverse gear

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    Yeah, whining does sound like the diff or bearing, but mine is very low pitch, rumble even, and does not change with speed... like someone drumming fingers on thick wood extremely quickly and is definitely coming from off-side, not central.

    I like the idea of heat shield resonating as mentioned by s3dave, as this sound seems to occur at higher speeds after extended motorway/spirited country driving. Logically thinking, it could be the shield heating up over time, which would change it's properties. After a long drive like that, sound at 40mph is more pronounced than usual. I did have a rear-end shunt from a biker a couple of years ago and had to tighten-up the back-box heat-shield up after repairs, as it was making sounds like the was about to fall apart - maybe this is a remnant from that.

    It sounds like I'm clutching at straws here, but I want to try and eliminate as much as possible myself before getting a garage loose on it :uhm:
    #7
  8. S3 Paul
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    S3 Paul Active Member Staff Member Regional Rep

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    Check the rear drive shafts for any play.
    Then... remove the back box and take off the heat sheilds for a test drive, re fit the rear box and go for a blast
    #8
  9. leshkin
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    leshkin Speeding in reverse gear

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    Thanks all - I think I'll work on eliminating the spacer and heat shields for now... will check the drive shafts also.
    #9
  10. S3 Paul
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    S3 Paul Active Member Staff Member Regional Rep

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    while the car is still sat on the road... see if there is any play in the shaft.
    #10

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