We've had our MCS for barely a month now and are experiencing a similar noise. It's a "whirring" from the right front (at least it sounds that way). At first NW Mini thought it was the serpentine belt, so replaced that. That didn't resolve it so we got a new water pump (we had a coolant leak so it needed to be done anyway, but we were all hoping it was related).
Took it back in last week and Steve tried replacing the belt again. No luck. He's thinking it may be a pulley problem at this point so we are getting ready to try that one. We've had this problem since day 1 and have yet to figure out the source. But NW Mini has been really good about trying things, squeezing us in when service slots open up and keeping us running.
Only thing we seem to have in common is that both cars are MCSa. Well that and both are CR/B - that couldn't be it, could it?
Michael & Jeanne-Marie
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'05 MCSa, CR/B, "CARMIN"