[Kirby64]

Similar mechanism as your attic noises. There's a giant metal plate on the bottom of the thing, so all the heat generated while it's supercharging (in a very cold environment) causes that 'snap' which makes a loud noise. Same thing happens if you've ever heated up a thin metal baking sheet. It'll 'snap' from one position to another and make a horrible racket.

Same thing apparently happens if you are heavy on regenerative braking when descending a mountain pass. Cold air, plus 50kW+ of regen braking is similar to just supercharging the car.

[flutas]

Something else interesting when supercharging in the cold...LOTS of steam(?) at times.

Shocked me the first time it happened. Cold (~5F outside), low and hot battery (just went from 80 to ~5%). Legit thought the car was on fire at first.

[Kirby64]

Never experienced the steam myself, although I can't say I've ever tried supercharging the car at 5F. Coldest I've ever done it was probably in the 40s, which is plenty cold enough to cause that popping sound when it's pulling 250kW.

[flutas]

Oh yeah, the popping was crazy loud as well.

Thinking back to it, the battery must have been extremely warm at the time too, since that 5F was after two hours through a 2 lane mountain road (crossing the range).

[alliao]

thanks! I've heard the pops during my winter trips but never associated with thermal expansion! Always thought I'd hit some animals or debris on the road.

[jacquesm]

Oh, that last one is an interesting one.