Ah yes, the noise has nothing to do with the group (unless the group and the hub happen to be the same). It has more to do with the brand of wheel and what kind of freehub they use. Some are noisy like Campy, Chris King, etc. Some are quiet like Shimano. Shimano is quiet because it doesn't have the same types of prawls that other wheels have. Other wheels need to click through each prawl, and the more prawls the noisier the wheel. Correct me if I'm wrong, but Shimano hubs don't need to "catch" like others on one of these when you start pedaling. So, when you stop pedaling there isn't so much of a clickclickclick noise as the hub spins without being engaged by pedaling.

If he's recently had the hub rebuilt, then unless someone just screwed up servicing it, then I wouldn't worry about it. Maybe that's the sound the wheel is supposed to make when in good condition. Also, if the hub was changed at all, maybe the new parts have a different sound than the original. He might want to take a peek and see if anything is loose, but since it's not a Shimano hub, I wouldn't worry too much about the noise.