it was posted on another forum, i believe mazda3forum.com not sure, but they had a sticky for the same question

 

Tracker... would you care to elaborate?

 

ive said this before...i cant really explain anything w/o me sounding stupid or people getting lost, but ill try *ahem*...When you turn on your A/C or heater, more gas is being forced out of the exhaust (works best with an aftermarket exhaust) so gives it a more deeper sound, when ideling or reving it thus getting rid of the ricey sound in the higher RPM's, also while driving youll feel a little jump in ~5K+ range, i dont know, thats the best i can explain it, all i can say is try it for yourself cuz it works for me, i know this works cuz when i was racing and i had the A/C on i felt the CAI kick in @ ~4200 RPM's and ~4sec before i redline shifted i felt another kick forward and i didnt hear that rice sound i usually get when im up that high.