Ampre Sand
Member
Did some exploration yesterday with the frunk liner removed. As far as I can tell, this low frequency tone is a sympathetic vibration in the cabin as the heat pump spins up through a certain RPM range. It would guess it's a pesky NVH issue that is a) harmless, and b) what's left over after really making the pump incredibly quiet (it really is). Stuff like this is like whack-a-mole to the engineering team. Given the sound is brief, I'd bet they even know about it and intentionally keep the pump's time in that RPM range as brief as feasible.
Cases in point: my neighbor's pool pump goes into high speed cleaning mode every morning at about 10AM. He can't hear it, but the frequency it runs through happens to match some resonance in my upstairs bedroom. Took me a while to figure out the source of the vibration. Similarly, the washing machine at the other end of the house causes my living room window to vibrate like there's an earthquake happening. No other vibrations felt anywhere - it's just a resonance that happens to match.
As an aside, the HVAC system under the frunk liner is a startlingly beautiful bit of engineering. I'm sure it will continue to evolve, as well.
Cases in point: my neighbor's pool pump goes into high speed cleaning mode every morning at about 10AM. He can't hear it, but the frequency it runs through happens to match some resonance in my upstairs bedroom. Took me a while to figure out the source of the vibration. Similarly, the washing machine at the other end of the house causes my living room window to vibrate like there's an earthquake happening. No other vibrations felt anywhere - it's just a resonance that happens to match.
As an aside, the HVAC system under the frunk liner is a startlingly beautiful bit of engineering. I'm sure it will continue to evolve, as well.