Faint "siren" Noise Upon Engine Start

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by broski, Jul 26, 2022.

  1. broski

    broski Junior Member

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    Hi All,

    I'd like to get some guidance as to what I might want to investigate with my 08 Prius. 80k miles. The symptom is a faint siren-esque noise (almost like there was a police car approaching from half a mile away) coming from the front of the car when the car starts. It is not audible once the car starts moving. It is reproducible but seems to be less present on a hot start. The noise will occur regardless of if the HVAC is on or off.

    Any ideas?

    edit: I should note. Coolant levels for the engine & inverter are both good. Serpentine belt was replaced last year.
     
    #1 broski, Jul 26, 2022
    Last edited: Jul 26, 2022
  2. bisco

    bisco cookie crumbler

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    is it the old fashioned siren or the newer euro style?
     
    #2 bisco, Jul 26, 2022
  3. PriusCamper

    PriusCamper Senior Member

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    Is is possible the serpentine belt that was replaced is when this noise began? Or soon as it was worn in? How does belt tension seems?

    Thinking you oughta get an auto stethoscope or hold a screwdriver up to your ear and pinpoint the source.
     
    #3 PriusCamper, Jul 26, 2022
  4. broski

    broski Junior Member

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    It's been about a year since the belt change, but I agree, perhaps the tension on the belt has gotten loose. My other thought was the idler pulley bearing starting to go. It's very faint but the sound is there. Perhaps I'll try and capture it.
     
    #4 broski, Jul 27, 2022
  5. PriusCamper

    PriusCamper Senior Member

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    I did an idler pulley on a Honda hybrid once. When you hold a long stick up to your ear with the other end on the pulley bolt if that's the problem it will be certain. You might need to take the right front wheel off to get access to it though.
     
    #5 PriusCamper, Jul 27, 2022
  6. broski

    broski Junior Member

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    Ok, some update here.

    I notice the sound changes if I shift into N, so it's likely related to the transmission mount I recently replaced. The mount was aftermarket and appears to be significantly stiffer/of worse quality than OEM as it transmits a very noticeable amount of noise over the old OEM one, even if that one was torn.
     
    #6 broski, Sep 12, 2022
    bisco likes this.
  7. broski

    broski Junior Member

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    Replaced the aftermarket trans mount with a proper OEM unit. Noise is gone and car is significantly quieter and comfortable. Never buy anything besides OEM rubber.
     
    #7 broski, Nov 27, 2022
    mr_guy_mann likes this.
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