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Discussion Starter #1
My new Mazda 3s Grand Touring HB has an odd hum.

This afternoon I updated the NAV maps, so I went into the car to reinsert the SD card. The car was in the garage with the door closed. The engine was not turned on, but the Infotainment was on. When I left the car, there was a faint hum that lasted about a minute or slightly less. I think it came from the front of the car.

I've heard it before, but only under these conditions where there is no other ambient noise.

I'd be interested to know if anyone else has heard this. Any thoughts on what it could be. I'm guessing maybe something in the lights.
 

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Yes, I've noticed this too on my 2014 iSport hatch and am guessing it might have something to do with the keyless entry system and/or an anti-theft system, or maybe the ecu; however, truth be told, I have no idea what it really is and would like to know. So, if anyone can enlighten us, it'd be much appreciated.
 

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It's the throttle body -- some solenoid of sorts. It's normal. My wife's 2009 Mazda 6 does it. My 2015 3 does it. Lasts about 45 seconds after every shut down. There was another thread about it a few months ago.
 

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I've never heard of a throttle body making noise, but I've never had a car with an electronic one. What would make a throttle body create a humming noise? I was going to guess that the fuel pump was staying on for a bit (assuming the sound only seemed to be coming from the front).
 

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Discussion Starter #6
I just went out to the garage to run an experiment. I turn on the electricals, but do NOT start the engine. When I turn them off and get out of the car I hear the hum. After about a minute, there is a click sound at the front of the car and the hum stops.

The hum does not happen if I don't turn on the electricals (ie, just open the door and close it again).

If I remove the key fob from the area around the car while the hum is occurring, it has no effect. I was trying to see if it was related to the locking.

The hum does not sound like anything mechanical (e.g. fan). It sounds more electrical.

Since so many experience it, I'm sure it is nothing to be concerned about. Cars sure aren't what they used to be.
 

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When the engine is off, if I turn on the parking lights there's no humming noise but if I turn on the stock HID headlights I can hear the hum. It went away as I turn off the headlights. Maybe it has to do with higher load on the internal electrical system?
 

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I just went out to the garage to run an experiment. I turn on the electricals, but do NOT start the engine. When I turn them off and get out of the car I hear the hum. After about a minute, there is a click sound at the front of the car and the hum stops.

The hum does not happen if I don't turn on the electricals (ie, just open the door and close it again).

If I remove the key fob from the area around the car while the hum is occurring, it has no effect. I was trying to see if it was related to the locking.

The hum does not sound like anything mechanical (e.g. fan). It sounds more electrical.

Since so many experience it, I'm sure it is nothing to be concerned about. Cars sure aren't what they used to be.
It still could be something like the fuel pump. It actually is supposed to come on before you try to start the car to build up the pressure for when you do.
 

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That makes sense to me, especially since you can hear the hum when you turn on the electrics, but not when simply opening/closing the door. It could be getting fuel ready for the injectors the next time you start the car (since there isn't a key turn to ON before START because it's all push button) or it got the fuel ready and has to let some of the pressure off because it wasn't actually used and the fuel shouldn't stay there.

I have no proof for any of this; Just thinking out-loud. I feel like I did read something along those lines in the manual.
 
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