Well, I went in for an oil change and just mentioned that there seemed to be a slight roaring sound at 20-30 m.p.h. and they said they'd check it out. It wasn't really that loud (quiet grumble sort of), but I wanted to have it checked out in case they could catch something, adjust the specs (I bought the car used, car now has ~10K miles on it), etc. They said leave it here for the day and we'll have new tires on it when you come back.

It all makes me a bit nervous as I've been looking to get 19" or 20" (haven't 100% decided yet) aftermarket wheels and tires.

 

"Nissan has determined that 350z front tires are sensitive to any toe-out condition; and if the front toe alignment is not correct on Model Year 2003 350Z vehicles, an irregular wear pattern on the inner edge of the front tires may occur. This wear pattern can cause a tire noise condition described as "tire roar" or "tire growl" which may be most noticeable during low speed braking. Rear wheel alignment is not affected."

this is a common problem, if you want to find out more try searching, tire feathering, tire roar, and anything like that and you should get plenty of info

 

I'm fairly familiar with the issue of feathering and the roar, just that...

1) I thought it would have to be more pronounced to get the tires replaced.

2) I didn't really know I had it, though there was a bit of grumbling.

3) I am looking into upgrading to expensive aftermarket wheels and tires and know there may be issues with Nissan replacing those.

#3 is my biggest concern.