Hello all. I just took delivery of my new Trek 5200 and it is a sweet ride. I noticed today when I took my test ride home that sometimes when I apply the front brake I could feel the steerer tube are shake a little bit. Upon further inspection when I got home I stood the bike up on the rear wheel with handle bars in hand and both hands on the brakes. When I do this and I push up and down on the bars, the steerer tube is a bit loose. It's not a huge amount, but it's definitely not tight.

My question is ... is this supposed to be like this? Is there a way to tighten the headset? I tried to turn the top piece of the headset, but it doesn't look threaded to me (my old bikes used to have threaded headsets that would remedy this problem)

Thanks!