I'm still not 100% convinced it's mechanical... it sure sounds electrical to me. I've heard all the arguments back and forth, but it just doesn't pass the "smell test" in my mind.
Mike, I'm not convinced you're wrong either. Let me say it another way... you might have a good sense of smell. Or maybe hearing. I agree there's an electrical component to this sound.
Here's why... using your right foot on the pedal you can change sound characteristics by quick choices of pedal position inputs, and you'll hear the sound respond far faster than the car physically responds by speed changes or even the feeling of thrust hitting your butt. Like a real quick sharp little jab and release of the pedal rewards you with screech variatiions but no driving dynamic change that is equally matched to the noise. You get a sense of power drivers pouring it in to the motor is what is making a complaint.
To me, this is an electrical driver sound that is doing PWM with gobs of power that is shaking inductors. It's like I want to cement some coils down to the printed circuit board more. I just can't imagine a rotor with the inertia of the one in a Tesla can change its rotational speed to make its bearing rotational sounds change pitch that fast. So these are not rotationally tied sounds is my conclusion.
But this doesn't mean the bearings are not also doing something nasty in a non-rotationally related way. i.e. they could just be chattering in their races. Vibrating as they rotate. Even within spec limits and tolerances of bearing clearances.. there is room between ball and race... and therefore vibration is possible. And I believe they could respond in their vibration frequency as fast as you can modulate the pedal. Because bearing balls are low mass in comparison to the rotor. The balls have become "speakers".
And if Tesla is finding that a bearing change removes the noise.. it points to mechanical issue (audible vibration) coupled with (induced by) the issue of being electrically driven. The bearing makes no sound when power is taken away (lift the pedal) because the electrical component is removed (reversed). Electrically induced Vibration stops. And if the races or balls have been worn, you'd never know it and cannot hear it.. these are silent bearings again.
New bearings have tighter tolerances (less space) between ball and race, so we don't hear the sound on new cars. But same frequency sounds could still be there at very low amplitutde, too quiet to hear. As the bearings get into their groove, so to speak, after many rotations and "loosen up" a bit... the sound moves in louder. More room to shake. But bearings could still be well within permissible limits... just making noise you can hear now. Louder as it ages more. But well within spec.
Micro pitting. Vibrations may wear the ball or race or both because it is like hammering metal on a tiny scale... flattening spots on the ball or race, or tiny bits of material fly off. This may cause bearings to wear faster than they otherwise would, tolerances opening up beyond spec.
Tesla knows this. Bearings are a wear item. Moreso on these crazy powerful high frequency driven things. Noise is just a nuisance while bearings remain in spec. But noise is an indicator of opening gaps. And like any other application, bearings making noise is an indicator of something wearing, not going in a good direction, and needs to be replaced before a failure. There is probably tons of "room" between what we hear as loud sounds from the DU and when a failure is likely to happen.
Tesla is selling a silent experience, but they can choose to stop doing that. It would be interesting to hear bearings that have just exceeded ther spec and actually need replacement to prevent failure. Maybe we're hearing that already? But maybe we're still hundreds of thousands of miles within that. The real determining factor is how loud can people stand it.
