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Rattle When Coasting

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by DDHART, Jun 18, 2020.

  1. DDHART

    DDHART Junior Member

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    I'm new here and searched for this topic but didn't find anything. If I'm in the wrong forum please let me know. I've got a 2010 with around 100K miles. A rattle has just developed and it appears to be under the car, perhaps near the centerline, and just in front of the rear seats, but of course it's hard to pin down. My wife thought it was right rear wheel well, so there's that. Small sample size, but it doesn't not appear to be there when I accelerate or when I brake, but only when I'm coasting. It's intermittent--maybe 60 percent of the time when I'm coasting--and when I step on the gas or the brakes it goes away. If I step on the gas it rattles just once and then goes quiet. IOW, I'm rolling downhill making the noise 60% of the time, and as I get going uphill I step on the gas and it rattles just once and then doesn't start again until I let off the gas. Going downhill on the brakes it doesn't make a sound, but this just started happening so like I said, I haven't experimented much with it and I could be wrong.

    It doesn't sound like it's coming from the engine compartment at all. I replaced the front brakes myself a couple months ago and haven't had a problem. I haven't yet touched the rear brakes and there's no brake noise at all.It doesn't sound like a CV joint and the rattle seems completely unrelated to whether I'm turning. The plastic pan under the body (splash guard?) rattles a little when I push on it, but it's a higher pitch and not so loose that I'd immediately suspect it. My wife first noticed it a couple hours ago at 50 or so MPH, and I just drove it around the neighborhood at 20 or so MPH and heard it as I've described. Thoughts? Thanks very much.
     
    #1 DDHART, Jun 18, 2020
  2. pjksr02

    pjksr02 Active Member

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    Something in the exhaust system, maybe a heat shield? Search around the site, as there have been some threads about the heat shield/exhaust system.

    Are you up-to-date with all the recaills of the 2010s?
     
    #2 pjksr02, Jun 19, 2020
  3. Grit

    Grit Senior Member

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    You’re in the correct side of the forum.

    Rear right wheel will flap?
     
    #3 Grit, Jun 19, 2020
  4. bisco

    bisco cookie crumbler

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    loose aero cover?
     
    #4 bisco, Jun 19, 2020
  5. ASRDogman

    ASRDogman Senior Member

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    Maybe a rock got onto a panel?
    You need to check EACH piece carefully. Tap on all the metal shields.
    But, it could be inside the muffler or converter that has come loose and is rattling.
     
    #5 ASRDogman, Jun 19, 2020
  6. DDHART

    DDHART Junior Member

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    You guys are great, thanks. I'll get it up on jackstands in the morning and poke around.
     
    #6 DDHART, Jun 20, 2020
  7. DDHART

    DDHART Junior Member

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    Welp, I got under it and poked and shook everything and didn't find a problem, so I took it off the jack stands and drove it and the sound is gone. I wish I could say it was me, but it wasn't. Thanks again for the ideas though guys. I appreciate it.
     
    #7 DDHART, Jun 20, 2020
  8. Peter123

    Peter123 Active Member

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    #8 Peter123, Jun 20, 2020
    pjksr02, Mendel Leisk and Raytheeagle like this.
  9. ASRDogman

    ASRDogman Senior Member

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    You should have checked any nuts or bolts holding the shields on.
    They could be loose, or it's rusted around them. You moving them around could have been
    just enough to stop the rattle...for now. :) But hopefully it doesn't come back.
    But if it does, you know what to look for.
     
    #9 ASRDogman, Jun 21, 2020
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