I own a Trek 1.5 road bike, purchased new around June 2012. The headset (original, never replaced) has recently been experiencing some interesting issues:
About 4 weeks ago, the headset began squeaking much more than normal and became stiff to the point that turning the front wheel was very difficult. Wrenching it from side to side would free it for a little while, but then it would resume the behavior fairly quickly (10 minutes of riding or less). I took in in to my LBS, they said "huh, odd," checked alignment, lubricated it, and said I ought to be good to go.
Things worked well for about two weeks of light riding, but then the behavior resumed- first the headset started squeaking more, then the steering stiffness returned. After turning the front wheel side-to-side for a little bit, the stiffness left and was replaced by a very loose feel. This loose feel and non-squeaking behavior stuck around for about 10 days, and then a few days ago, the headset started tightening up again and squeaking very obviously.
I'm interested in potential explanations for the symptoms observed and potential fixes. The reason I'm coming here first is because I'd like to have some more information before going in to the bike store for the second time- I'm after a permanent fix, not just a check/lube/out the door. My guess is that something's wrong with the bearing unit inside, but I'm not sure.