Whats is this sound

Sounds normal to me i think, i think i hear that sound when the car is idling, likely coming from the electric motor.

 

Sounds to me like a bunch of air molecules bumping into each other at resonance frequencies to create a phenomenon we know as "Noise"

 

Mine does the same.

 

That's the inverter. That's how it sounds. Its workin' hard! Its under that big silver cover. The fluid reservoir to its left is the fluid that keeps it cool. it needs to be changed now and then very important.

Now go turn on the AC on high and listen to it SCREAM!!!!.

 

That baffled me in my Gen 3 for the longest time.

Get 'cherself a mechanic's stethoscope and touch a few places. Make sure one of them is the throttle body. Then you'll know. That was what it took for me to stop being baffled.

The throttle body has an electric motor to move the throttle plate open and closed. Most of the time (like when the car is just sitting there stopped with the hood open), the ECM is just using the motor to hold the throttle still in one position. The way it does that is by sending a constant train of electrical pulses to that motor, where it adjusts the width of the pulses until the throttle is staying in the target position.

That train of pulses, being sent to a motor after all, makes a little bit of motion, at the pulse frequency, which is the sound you're hearing. But checking it with a stethoscope (or even a long screwdriver pressed tight to your ear) will convince you a lot faster than me droning on about it.

I think it's kind of funny that the ECM continues actively controlling the throttle position even when the engine is stopped. But so help me, it does.

Other places your stethoscope will pick up the same sound surprisingly loudly (though not as loudly as at the throttle body itself) will be on some of the engine coolant hoses and especially the sections of metal pipe. The throttle body is in the coolant circuit, and water is a fierce conductor of sound (as any diver will tell you).