Disc brakes are very precise and the pads run very close to the disc even while not braking. Due to this, even small misalignments might make the pads (or even the caliper) rub against the disk, producing the noise you describe.
A simple test would be to lift the wheel (or turn the bike upside down) and spin the wheel slightly. If it stops quickly, the brake is rubbing. Try to visualize where this rubbing happens.
If it is actually rubbing, you have three alternatives:
- If it is a pad, you can adjust the pads yourself. This procedure depends on the brake type (hydraulic vs mechanic) and model;
- If it is the caliper, you can reposition the caliper by releasing the bolts attaching the caliper to the rest of the bike (directly or via an adapter), and reposition the system. Sometimes, braking hard is the best way to force the caliper to stay in the position it should, but this often require some fine-tuning.
- Take the bike to the shop where you purchased. Since the bike is new, they it is very fair that you have it serviced.
Now if the wheels spin freely, or rub against something else, well that would be another story.
Hope it helps!