i just bought my bike about a month ago, put about 400km on it so far. today i noticed tha back wheel had a wobble to it (only word i can think of to describe it). is this a case of the wheel not being true? or is it some other adjustment? its an ever so slight wobble but it annoys me. any suggestions, advice would be great.

Yes, it needs to be trued. Take the wheel to the bike shop. They will true it for a few dollars.

The advice is good, but actually there are a couple of explanations. I noticed my new bike's rear wheel wobbling today too. In my case it was poorly adjusted cones. If you lift the back of the bike and spin the wheel and you can see the rim move closer and farther from the brake as it spins, it's out of "true". If you grab the wheel and you can rock it a bit from side to side, its the cones. These cones are on the axle and point inwards. The hub has horn shaped sections that point outward. They fit together sort of like sticking the point of an ice cream cone into the end of your trumpet. Steel balls are set in a layer of grease between the hub and the cone on each end and the wheel rotates on them. The balls bear the weight of the bike, hence "ball bearings" The bike shop can adjust the cones slightly closer together if that's the problem.
Robert

its exactly a case of moving closer and further from the bake pads......i'll swing it by my bike shop and have them true it...thanks!

wow. i got my bike 4 days ago and am having the same problem

If you've changed the inner tube, is it bunched up in one place? When I'm in a hurry, I don't put the inner tube back in the tire correctly, and it ends up being a bit of a mess with the inner tube bunched up just at the valve stem. What the Park Tool guy told us to do is deflate the tire, push the valve into the tire, then pull it back out and reinflate. It always works for me.

Koffee