57MPH Hum

Wondering if anybody else has seen this too — well, heard it, actually:

Over the past couple months or so, on my 2017 ‘Prime Advanced, with 66,741 miles, as I accelerate through 57MPH, at around 54MPH, I start hearing a … hum? As my speed increases, it peaks at around 57MPH, and then trails off, until at 60MPH or so, it’s pretty quiet again.

Observed qualities:
— Even at its 57MPH peak, it’s not overbearingly loud, but only slightly annoying.
— It’s much quieter in hybrid mode than in EV mode, so it’s presumably some sort of resonance in the electric drive train.
— It’s probably pitched at roughly the Eb above middle-C on the piano.
— Its probably fairly sinusoidal-ish.

Anybody heard anything like that?

 

Reasonable question, but no, definitely not tires:

When I ease off the accelerator so as to hold at 57MPH, rather than accelerate through 57MPH, the volume of the sound goes down.

Also, as I mentioned, it’s quieter at the same speeds in hybrid mode than in EV mode.

It seems to be related to how much power the MGs are producing in the speed range.

 

Oh, I also haven’t been able to isolate the direction the sound is coming from, so far at least.