My engine's intake system is completely factory stock. I've never thought about the whistle coming from the intake. I'll do some experimenting this weekend with different gears and throttle positions to see if I can duplicate the noise like you have in your car. I'm having a Mazda dealer look at the car on Monday. This dealership (not the one I bought the car from) has so far been helpful in fixing some interior rattles and a faulty clutch pedal assembly. Maybe they can help on this issue.

 

After doing some research on another forum (http://www.mazda3forums.com), I've learned my issue is shared by others. I can't find any information on a cure, of course. Just bad engineering, I guess.

I live in the Phoenix, Arizona area and most of our freeways have rubberized asphalt that substantially reduces road noise. Therefore, engine and transmission sounds are much more audible. I can tell you that the whine I hear at 60-65 mph in my Mazda3 is piercing. I have heard nothing like it in any of my previous cars with manual transmissions, including two late-model Honda Civics, one Toyota Corolla, a '65 VW Beetle and an '80 Jeep Cherokee -- all driven to well over 100,000 miles.