Lately I've been having a noise when at freeway speeds, that *seems* to be coming from behind the dash on the drivers side. It sounds just like a "warbling" fan motor pushing air, but changing my heater settings doesn't seem to change anything. It's very noticeable above ~3k rpm, and subsides when I let off the throttle, especially if I let it dip below the 3k rpm mark. I've got a few other little problems I'm slowly working on, but this one has been bugging the hell out of me seeing as the Mini is my daily driver in the winter months.

I've also been throwing a pre-cat O2 sensor code (P0130), and was wondering if it might be a vacuum leak somewhere, but if that were the case, speed shouldn't play a factor, as I can't replicate the sound in lower gears at similar RPM.

Oh, she's an '05 base model with around 155k.

Any advice from the Mini gurus? I'm fairly keen with engines, but mostly play with motorcycles and classic cars.

 

I have same problem, I think mine is the AC compressor or something related to it. Do a search on AC Whine or AC noise, lots of people with this..see if that might be it. Even in cold climate with Auto Climate AC compressor will still engage sometimes when heat is on.
Good luck, I have resorted to cranking the tunes.