What exactly is a microfilter for? From what I see it's to with some sort of air filtration etc, but how does it work? The reason I ask is that the service interval on the I-Drive screen for the microfilter is dropping in mileage at least twice as quickly as the oil, brakes etc. The oil has shown 6000 miles remaining for a good while now (more than 1000 miles) and the microfilter has dropped from 8000 to 5000 in the same space of time. Is there any reason why this is happening, anything I should look for?