After getting home today, I noticed a new noise coming from behind the right-rear wheel. I've never heard this sound before, and it was remotely like the sound of a cooling fan on a computer...But cooling what? I know what the fuel pump sounds like when it's priming, as well as the radiator fan and the EPS fan. I've searched around other forums to no avail. And the fan shut off before I could locate the source.

Does anyone have the slightest clue what it could possibly be?

 

Is you Mini a S? Mine makes the same noise. Im not 100% sure but I believe it is a electric pump that moves the coolant around in the car until it cools off because of the turbo. Hope this helps.

 

I've correlated this sound (coming from the same area) to when my fuel level is low, but never figured out what it was exactly ...

 

Same here, before I gassed up yesterday I heard that sound in the right rear. I only had maybe 1.5 gallons left, I was walking around my car when I heard it. I've heard that sound many times before, it must be some kind of fuel return of pressure relief or something.

 

If you open up the pass side trunk panel there's some sort of electrical wizardy back there; I always assumed that was the source of the noise. On mine, the noise coincides with the trunk release spontaneously triggering, opening the rear hatch. I'm going to diagnoses it more this soon, I'll put something up if it turns out relevant.