Don't worry for a second about the noise you hear at low rpm and partial throttle. It is simply intake noise. You are actually hearing the air/fuel intake mixture process. It means your 'Stang is healthy and just waiting for you to give it a little more gas! I know when I got my 2001 V6 I also noticed that sound right off the bat. I was taken aback before I realized what it was and confirmed it.
Now just go out and enjoy that beautiful car!
