No, the wheels are the standard touring alloys and have never been refurbed. Chances are, it's a build up on one of the pads. I had a similar problem on a Mk1 MX5 and it was only whilst slowly rotating the wheel by hand whilst the car was on axel stands, that I felt a part of the disc catch as it passed under the pads. I took the disc off and gave it a quick sanding, that solved the problem.
i am hoping its the same with the 350z discs, but as I need to take the wheels off and clean everything up, it makes sense to buy pads and change them over at the same time.
when ever I buy a car, I always carry out a full change of all the fluids, plugs, filters and break pads. That way I can start my own service history and I know what needs changing and when.