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Thread: What causes an exhaust to "hum" or "growl" when letting off the throttle?

  1. #1
    Join Date
    Jan 2013
    Location
    New Jersey
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    E36 M3

    What causes an exhaust to "hum" or "growl" when letting off the throttle?

    Like this car. The sound I'm talking about can be best heard at :47

    Last edited by Aestheticus; 09-11-2014 at 05:29 PM.

  2. #2
    Join Date
    Jan 2004
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    Kentucky
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    '03 Z4, '06 Forester
    He's in gear slowing down: there is no fuel being injected .. the engine is being spun by the wheels/driveshaft (instead of the other way around), which makes it sound different in itself. Add in the fact that this guy is braking (somewhat quickly) and you get the sound of the engine spinning (without any combustion going on) rapidly slowing down, which sounds like the hum you hear.
    Last edited by slocar; 09-11-2014 at 08:24 PM.

  3. #3
    Join Date
    Mar 2007
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    SD, Cali, USA
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    1995 M3, 1985 745i , S13 240sx sr20det
    I hear no hum. Are you referring to the staccato percussive sound?


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  4. #4
    Join Date
    Jan 2008
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    Arida Zona
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    z3
    thats what happens in a manual car when you rev it up and get off throttle without shifting

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  5. #5
    Join Date
    Dec 2013
    Location
    Springfield, IL
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    1995 BMW 325is
    It's a combination of everything stated above, and the doppler effect.
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