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    jzhou Junior Member

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    My Prius IV with about 10K miles started to emit a high-pitched electrical humming sound under the hood when it was in Ready mode. It did not have this sound before. I opened the hood and found the sound was coming from somewhere around/under the engine area.
    I want to know if this is normal on Gen 3 Prius?
    I have seen post on the same noise in Gen 2 Prius but the posts (thread) stopped without a resolution.
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    2k1Toaster HID Guru

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    Sure its not the inverter you are hearing?
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    jzhou Junior Member

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    No. Double checked and it is coming from the Engine block on the left side. While the inverter is on the right side.
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    spinkao New Member

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    I hear the same sound coming from my gen II, especially when the car is quite hot (standing in a parking lot in direct sunlight). It disappears/gets less audible as things cool down. I guess it might be the inverter coolant pump.

    Is the occurrence of the sound you are hearing also temperature-related? Do you hear it (or perhaps is it less noisy) when the car is cold?
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    GrumpyCabbie Senior Member

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    And it's definitely not the a/c compressor which when running under high load (especially when first started up on a hot day) can almost sounds like an electrical sub stations hum/buzz.
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    bwilson4web 03 and 10 Prius

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    I don't hear it with our ZVW30 Prius.

    Does this happen when the car first starts, all the time, or after it is warmed up?

    Is it there when the engine is off?

    Do you have a way to record the sound into audiacity for a spectral analysis? That package has the ability to filter out some of the noise and you could quantify what you're hearing (i.e., frequencies,) it could help.

    The auto stores sell stethoscopes with probes used to isolate noises. They don't cost much and can help identify the source. Be sure and pull the plastic, engine cover off to help identify the source.

    Since these are external noises, you might enjoy reading the NHTSA report "Quieter Cars and the Safety Of Blind Pedestrians: Phase I", DOT HS 811 304, that can be downloaded from the NHTSA .gov web site:
    Although there is new data, empirical sound measurements, the study repeats the same flawed statistical data of the earlier NHTSA report about relative hybrid risks.

    The interesting part that relates to this discussion are the external spectral analysis, pp. 49-51 that shows the Prius generally has lower, high frequencies. What this means is outside of the car we would tend to hear more lower tones with the Prius than the reference Matrix. But you're hearing a noise with the hood up?

    Bob Wilson
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    jzhou Junior Member

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    The car is just turned on in the Garage and the A/C is not running or turned on. The outside temp is on the 70s F.
    The operation sequence was like this:
    - turn the car on to Ready mode
    - After 5 seconds, the ICE runs
    - After 20-30 seconds, the ICE stopped
    - The humming sound is audible

    The car is in Ready mode and the Transmission is in Parking all the time.
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    jzhou Junior Member

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    Thank you, Bob.

    The sound is loud enough without the hood open. I will record it with a video recorder later today.

    Thanks for the Audacity information. I will give it a try if I have time. But I am more worried if this thing is not a normal behavior. If it is not happening on all the Gen III, then I will take the car to the dealer for a check.
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    Colonel Ronson New Member

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    i get a sound i hear from the hood every time i open the drivers door. i assume its just the car getting ready for me, and im assuming that its normal. does everyone else get a sound when they open the drivers door?
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    Patrick Wong DIY Enthusiast

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    Electric engine coolant pump?

    Do you also hear the sound produced by the inverter?
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    bwilson4web 03 and 10 Prius

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    Hi,

    This evening I hear what sounds like the inverter pump. So I did the following:

    • hit power without brake, accessory mode - no noise
    • hit power second time without brake, ignition mode, instruments light - no noise
    • hit power with brake - the humming noise
    On my car, it is the inverter coolant pump but I can't see it easily.

    Bob Wilson
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    jzhou Junior Member

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    I made a 60MB video/audio file of the engine noise in quicktime format, but it seems I have a hard time to upload it to the prius chat. What should I do?
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    2k1Toaster HID Guru

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    60Mb? Compress that... Use H.264 compression if you want small size and HD video. Since video isnt that important, I would compress it with FLAC audio and low bitrate video.
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    jzhou Junior Member

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    Would appreciate if you can name some free software packages that can do the compression as you stated? Thanks.
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    2k1Toaster HID Guru

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    I dont use free software to do that, I use Adobe Products...

    But a search on google for "free h.264 encoder" found this site: H.264 Encoder - freeware encode video to H.264 format

    Looks promising. However like all free software I would suggest running it in a virtual machine with a virus scan after you download it before you transfer it to your main computer. Use at your own risk.
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    bwilson4web 03 and 10 Prius

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    Sorry but 60 MB is way too large. The most that is needed would be a short, audo clip from the file. In my case, I have iMovie and QuickTime which have the ability to edit video and extract audio.

    I loaded an iMovie with a 7 MB phone clip but the cicadas were too loud. I'll have to find a quieter place to try again.

    Bob Wilson
    1 people like this.
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    jzhou Junior Member

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    Ok. Youtube solved my problem. Here is the link:


    I was trying to kill a fly with a cannon:D
    I may still try the "audiacity" to do a frequency domain analysis on this sound. The signature of the frequency may tell us if this is one of the normal characters of the Prius sound spectrum. Thank you, Bob.
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    bwilson4web 03 and 10 Prius

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    Hi,

    For those trying to listen, use ear-buds or other high-frequency head phones. The sound you hear is exactly what I believe is the inverter coolant pump. But the proof will be finding it and co-locating a microphone. I'll try to do that this evening.

    Bob Wilson
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    2k1Toaster HID Guru

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    The audio has been manhandled too many times to be of any use.

    Taking a 60Mb video, and compressing it on Youtube does not make for good audio analysis. This of course is assuming the point-and-shoot camera you used had an above horrible microphone and it would make any difference.

    But converting from MOV-->FLV-->FLAC is just bad, and makes the outcome unusable... I suggest you export a losslessly encoded audio stream only from the video you have and post it so we can analyze it.

    [IMG]
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    tt2ride New Member

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    I have my Prius for 2 days now and I hear the same noise. I am also wondering what this is all about. Normal? Thanks.

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