I actually have a g35 but found this forum when browsing the net and saw there is alot of activity here so figured i could get an answer in a decent amount of time.
Here's my situation:

Picked up a 06 G 6mt and it has hawk pads and +XD rotors from brake-pros.com. When slowing to like 30mph and less the brakes are soooo loud! Before i took it home, i had the dealer put on the original rotors and he left the hawk pads on. I'd like to put these other rotors on because they stopped much better but they were way too loud? They have aboue 6-8K miles on the pads and rotors. What's the deal with them? The hawk pads are still on and the car still makes some noise from like 20mph to about 5mph but nearly as much. Is there break in period or do i just have terrible rotors? And also, how much more performance wil i get from putting on the crossdrilled rotors versus just leaving stock rotors with the hawk pads? Thanks
Dan

 

to answer your question...
the noise is probably due to your hawks pads and rotor condition. i replaced my stock front pads with oem pads at about 16k miles when it started to squeak a little at the light and the problem went away.
i recently replaced the front rotors with R1concepts drilled/slotted at 28k miles and they make absolutely no noise whatsoever after bedding them in.
Davidv's R1concept thread has plenty of info btw.