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Thread: HELP! Mystery chirping/squeaking noise

  1. #1
    Member janos_z's Avatar
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    HELP! Mystery chirping/squeaking noise

    My 500E has developed a mystery noise that two mechanics and an exhaust shop have been unable to identify (and they are getting annoyed by the fact that I'm not letting this drop).

    Here are the symptoms:

    1) When the car is rolling, there's a noise I can best describe as the kind of high-pitch squealy/chirpy noise that a library cart or utility dolly with un-lubricated wheels would make. A sort of warbly, garbled, squealy, chirpy noise. I wish I could upload audio of it.
    2) It's pretty audible outside the car; it can also be heard inside the car. Best heard at low/moderate speeds (like 15-30mph) though I've noticed it on the highway too.
    3) Seems to come from under the car, mid-line
    4) Happens almost exclusively when giving the car throttle (especially light to medium throttle; heavy throttle not so much) -- if I take my foot off the gas and let the car coast, noise stops immediately
    5) EXCEPT when rolling to a stop, while moving like 2-3mph, you can hear the noise again even if foot is off the gas as the car rolls to a stop
    6) Applying the brakes has no effect
    7) Car MUST be moving -- revving engine while standing still yields no noise
    8) Also, car has to be WARMED UP for this to occur -- usually 15-20 minutes after starting to drive; once it appears, it stays until car sits and cools for a while.

    So: rotational chirpy noise that's much more pronounced when giving it gas gently while car is in motion; can also hear it at very low speeds while coasting to a stop even if no throttle is applied; no noise when revving engine while stopped; audible both inside and outside car; car must have been driven for 15-20 minutes at least for the noise to appear (and once it appears, it stays).

    Car's performance doesn't seem to be affected. Yet.

    I'm thinking this might be a something having to do with the differential, given that it's both movement- and throttle-related. But it's not the kind of gear whine I'm familiar with from previous run-ins with a bad diff, nor is it the kind of droning that I'd expect from a bad wheel bearing (nor would I expect a wheel bearing to care whether or not I'm giving the car throttle).

    The car is pretty much in perfect shape otherwise, so this is driving me a little batty. Anyone who can help me solve this will have my eternal gratitude (and a round or two of drinks on me, if you live in the Bay Area and feel like meeting up!).
    Janos Z

    Current: 1993 500E ~ 1989 560SEL

    Past: 1993 500E ~ 1993 400E ~ 1994 E320 wagon ~ 2007 C230

  2. #2
    E500 Apprentice Guru
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    Re: HELP! Mystery chirping/squeaking noise

    Any work on the wheels where the dust shields got bent?
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
    199/268
    2014 E350 Cab 799/264

  3. #3
    postwhore posterchild Klink's Avatar
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    Re: HELP! Mystery chirping/squeaking noise

    Consider the seals of the driveshaft center support bearing, and the two rear wheel bearings. These noises sometimes come about from the seal breaking free from the intended stationary side, while adhering to the intended free side. On the center support, this usually means the center adhering while the outer surface breaks free, and on the rear wheel bearings the outside adheres, while the center breaks free. If the shop doesn't have a set of contact microphones ("Chassis Ear" or similar device), soak the center support with a non-rubber damaging thin lubricant (I like CRC Power Lube) and see if the noise subsides. If it does, replace the center support bearing assembly.
    Putting the fun in dysfunction...

  4. The Following 3 Users Say Thank You to Klink For This Useful Post:

    gsxr (1 Week Ago), janos_z (1 Week Ago), nocfn (1 Week Ago)

  5. #4
    .036 Hoonigan™
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    Re: HELP! Mystery chirping/squeaking noise

    I think Klink is correct. Note the driveshaft spins ~3x faster than the rear wheels, if you can determine the frequency of the noise, you may be able to pinpoint if it's coming from before or after the differential.

    Dave M.
    1997 E420 (Bugeyes)
    1994 E420 (Blondie)
    1994 E500 (Q-ship)
    1992 500E (Mach 5)
    1987 300D (Sportline Stage 2)
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    janos_z (1 Week Ago)

  7. #5
    Member janos_z's Avatar
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    Re: HELP! Mystery chirping/squeaking noise

    Thanks for the suggestion. Sounds like the center support bearing is a prime suspect. My mechanic did inspect it previously, but maybe not closely enough. I'll have them take another look and I'll report back.
    Janos Z

    Current: 1993 500E ~ 1989 560SEL

    Past: 1993 500E ~ 1993 400E ~ 1994 E320 wagon ~ 2007 C230

  8. #6
    postwhore posterchild Klink's Avatar
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    Re: HELP! Mystery chirping/squeaking noise

    Quote Originally Posted by janos_z View Post
    Thanks for the suggestion. Sounds like the center support bearing is a prime suspect. My mechanic did inspect it previously, but maybe not closely enough. I'll have them take another look and I'll report back.
    This problem can almost never be "seen" It can usually only be heard...
    Putting the fun in dysfunction...

  9. #7
    E500 Apprentice Guru
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    Re: HELP! Mystery chirping/squeaking noise

    My nasty Quirky noise left after that bearing change with the flex disks.
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
    199/268
    2014 E350 Cab 799/264

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