When I had just a CAI in my GT, you could hear more sound from the air coming thru a larger filter and more open plenum. You hear it most at WOT. You won't hear much difference at traffic speed or cruising. The stock system being a closed plastic system is of course much quieter.
One thing I guarantee you'll hear with a CAI and a tune is rubber burning off your tires.
Mine had a wider sound at the tailpipe when I put my foot into it, but sounded stock under casual acceleration. It had almost a "stereo" effect that lasted a few seconds, while accelerating hard.
The reason I ask is that on my G35 coupe, I put a conical filter in place of the air box and noticed a very annoying whistle when you pressed the gas. I don't know if it was just that particular filter's design or what, but it was so annoying that I put the stock box back on. However, at WOT the engine had a very aggressive growl to it. It was MUCH louder than the stock air box. It does not sound like the CAI and tune for the mustangs has that same effect.
Thanks guys. Someday I'll get around to the CAI and tune, but I'll be happy with a more aggressive exhaust note for now I think. Looking at the pypes violator...
Was your G35 a turbo? The sound you describe sounds like turbo/blower whine. I have a similar "issue" on my stang. Though it was an issue I am glad to have installed.