High pitched interior noise

Bought my Taco used about 2 months ago. So far so good, except one little thing that started bugging me about day 2.

When sitting in the driver's seat, at times I hear a really high pitched humming/whine - it is electrical in nature, and I have to have my head in just the right (wrong) position to hear it. Unfortunately that position is pretty much my normal driving position.

It is a very faint sound, up around 5000-7000 hz, it is a constant sound.

Does it with the motor off as long as the key is in the Run (2nd click) position. It does not do it with the key in the 1st click forward. It does it with the radio completely removed, the rearview mirror removed, the AC control panel removed and the AC fan not running, and the digital clock panel unplugged.

I've done no interior electrical mods so far - it did this completely stock.

I've heard electronics do this sort of thing before - my wife's garmin's cigarette lighter adapter does something very similar. Sounds like a step down transformer whining or something.

Having a hell of a time tracking this down - wondering if anyone has run across it - I tried searching but found mostly mechanical issues with drivetrain/accessory belt/bearing issues, which is not the case here.