Uneven disc brakes

My disc brake on the front wheel has got what seems like uneven friction
when the wheel turns. When I ride the bike it feels like the bike is
wobbling back and forth when I apply the front brake. If I stand beside the
bike and push it slowly back and forth I can feel the brake slipping and
gripping again as the wheel turns. A visual inspection does not reveal any
obvious problems e.g. eccentricity of the disc. What could be the cause of
this brake problem?



The bike is brand new, I have only ridden 20 km or so on it. Is this
something that will go away by itself when the disc and the brake pads get a
little more worn?



Any help appreciated.

Arild