Your aspect ratios are fine. There are x3's that come out of the factory with 17's and the sport with 18's and others with staggered set ups , in essence +1 . Ecu has nothing to do with figuring out your tire size unless the rolling diameter is completely off, which in turn would trigger the ABS light to turn on . I am confused with your assumption that the ECU is the caused of your driveline noise .

http://www.miata.net/garage/tirecalcold.html

Did you change just the tires or did you buy a new set of wheels and tires? if so , changed back to OE's see if you get the same " driveline noise"....I think you are just getting tire noise. Dont know about the new pirellis , but they are known for tire noise. Had them years back and disliked them for that reason.