Thread: Downshift/Acceleration Rattle

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  1. #1 Downshift/Acceleration Rattle 
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    Hi All,

    I've had this issue for quiet a while but had always chalked it up to the cat heat shield - until that flew off on the highway and the noise persists.

    It is very repeatable if I wait for the car to shift into 2nd then I get it to downshift into 1st. I'm pretty sure it happens from 3 to 2 as well its just not as easy to hear at higher speeds. It also happens sometimes if I bump the accelerator without a downshift but still accelerate moderately.

    It is a metallic, rhythmic rattle - it appears suddenly and seemingly fades over a second or two. In my mind, it seems to have something to do with the jarring off the engine/trans as the down shift occurs.

    It is especially noticeable it I am driving near walls, fences or concrete barriers as the sound is reflected back to me. It really sounds terrible and janky as hell.

    Please advise or share ideas ... thanks!

    EDIT: The rattle is probably about as fast as someone can sputter there lips if they are fed up with something. Bit slower maybe.
    Last edited by stocker; 07-26-2016 at 02:09 PM. Reason: rattle speed estimation
    2008 Grand Prix Base: Engine cover delete , flipped dogbone bushings, Transgo shift kit, Hayden 403 trans cooler,
    Quote Originally Posted by Yarbeau View Post
    we are all anal about our vehicles. Otherwise we would not be on an extinct platforms forum debating 3000 dollars cars!
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  2. #2 Re: Downshift/Acceleration Rattle 
    Killa Bee Scottydoggs's Avatar
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    theres a heat shield on the manifolds too.

    the exhaust could be doing it, check all hangers, or maybe even bad lower engine and tranny mounts.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  3. #3 Re: Downshift/Acceleration Rattle 
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    Quote Originally Posted by Scottydoggs View Post
    theres a heat shield on the manifolds too.

    the exhaust could be doing it, check all hangers, or maybe even bad lower engine and tranny mounts.
    Motor and Trans mounts are new within a few years. I'll check the manifold shield and the hangers - any recommended way of checking other than banging on things with hands or a rubber mallet?
    2008 Grand Prix Base: Engine cover delete , flipped dogbone bushings, Transgo shift kit, Hayden 403 trans cooler,
    Quote Originally Posted by Yarbeau View Post
    we are all anal about our vehicles. Otherwise we would not be on an extinct platforms forum debating 3000 dollars cars!
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  4. #4 Re: Downshift/Acceleration Rattle 
    Killa Bee Scottydoggs's Avatar
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    the whole exhaust will wiggle around a little bit, a lot if the mounts are worn out or missing. you can push on it with your foot to see if if makes any sounds.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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