Strange... we have a Mazda 3 as well, and at speeds over 80 I seem to notice some additional noise compared to the stock RS-A tires. Not bad, but I can tell it's there... I don't notice any kind of vibration, just a type of low frequency oscillating noise. This is on hubcentric steelies bought from TireTrends BTW.
Other than that, the change over to the KW17 has been pretty transparent in urban driving for my parents (which is a good thing).
No chance to test it out on snow yet, but who knows since the Vancouver forecast calls for flurries by the weekend....