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I have had my 2017 500e a month now.... I have noticed a few times (several times day before in stop and go traffic with a/c on. 100f showing on outside temp.)

A rather loud humming noise coming from under the vehicle?? (I think) speed seems not to matter but every time it's done it it stops when I've come to a stop...... any ideas I haven't a clue and it's to inconsistent to find.
 

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2013 FIAT 500e
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You know about the brake pump, right?

If it's not that, it's probably the A/C compressor. Since it's on the left, just ahead of the front wheel, you should be able to hear it cycling on & off when stopped, especially if you open your window (& any nearby gas cars have the new "shut off when stopped"). In fact, you can reach in & touch it to feel it cold if it's been running.

Next time you hear it, try momentarily turning A/C off to see if the noise stops.
 

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You know about the brake pump, right?

If it's not that, it's probably the A/C compressor. Since it's on the left, just ahead of the front wheel, you should be able to hear it cycling on & off when stopped, especially if you open your window (& any nearby gas cars have the new "shut off when stopped"). In fact, you can reach in & touch it to feel it cold if it's been running.

Next time you hear it, try momentarily turning A/C off to see if the noise stops.
Resurrecting an old thread here, but I just noticed this myself. We've had some warmer weather, so I've been using the A/C. How loud a 'hum' is it supposed to give off? I can just about feel it through the brake pedal and steering wheel when I'm running it.
 

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A couple years ago I posted a vid with sound (link below), & if you look through that thread I also posted some dB readings from phone apps:

 

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In order to know that you're not just hearing/feeling the brake pump, you can easily teach yourself what that's like. Just turn the car on with the A/C off & pump the brake pedal a few times. The pump will "buzz" & vibrate to bring the pressure back up after every 3 hard pedal presses, or 5 softer presses.
 

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In order to know that you're not just hearing/feeling the brake pump, you can easily teach yourself what that's like. Just turn the car on with the A/C off & pump the brake pedal a few times. The pump will "buzz" & vibrate to bring the pressure back up after every 3 hard pedal presses, or 5 softer presses.
No, it'a definitely not the brake pump. The sound and vibration are similar, but whereas the brake pump cycles off the A/C sound is continuous - even when I'm in stopped in park. Just went outside and turned the A/C on to listen again. It's quieter now, but that's what I was expecting as it seemed to get louder the longer I drove with the A/C on.
 

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OK, so here's a video with sound. The car is in Park with A/C on and fan at lowest setting. It's not the fan because the sound is constant no matter what the fan setting:

 

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That sounds to me about like mine at the highest point of its cycle, around 5 seconds into the video I linked above. You may learn more from that other thread, such as dB readings, but here's the direct link:
Also note that mine may not have cycled as high as yours, since it was in my cool garage so it didn't have to work very hard. You can hear mine cycle down pretty low after only about 30 seconds.
 

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That sounds to me about like mine at the highest point of its cycle, around 5 seconds into the video I linked above. You may learn more from that other thread, such as dB readings, but here's the direct link:
Also note that mine may not have cycled as high as yours, since it was in my cool garage so it didn't have to work very hard. You can hear mine cycle down pretty low after only about 30 seconds.
Yes, I did see the other thread, thanks. Seems like the consensus was that this was all fairly normal. I haven't measured my dB, but it sounds louder than yours. I'll keep an eye on it to see if it gets louder. What is it exactly that's making the noise though? An internal fan/bearing in the compressor? Not an expert in A/C...
 

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The sound is just the compressor pump. It's been a while since I've listened to a gas engine, so it might be interesting to open the hood of one & have someone turn the A/C on & off to see how its compressor pump sounds, if you can even hear it over the engine noise. Or compare to a different EV.
 

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2017 Fiat 500e (Billet Argento), 2015 VW Golf Sportwagen TSI 5MT (Tungsten Silver), 2002 Honda VFR
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No, it'a definitely not the brake pump. The sound and vibration are similar, but whereas the brake pump cycles off the A/C sound is continuous - even when I'm in stopped in park. Just went outside and turned the A/C on to listen again. It's quieter now, but that's what I was expecting as it seemed to get louder the longer I drove with the A/C on.
The compressor works in a linear fashion as blower fan speed and ambient temperature. If you had fan speed low like 1-2-3 it cycles on and off softly and compressor spins slower but 4-5-6+ the compressor is running full speed and makes quite a racket besides the cooling fan which get loud and aggressive. Next time on a hot day put the blower to higher levels and you’ll notice it gets louder and more buzzy.
 
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