I bought my Trek 2.3 back in mid July, and after a hundred miles or so I noticed that I was getting a creaking sound when standing to pedal. Took it to the LBS that I bought it from several times, they did a bunch of things around the BB like lube it, lubing the chain ring bolts, etc. Never fixed it. A few weeks ago I discovered I can duplicate the creak by pressing down hard on the handlebars, then lifting up on the handlebars while standing beside the bike. The creak occurs when I lift up on the bars.
So I tried loosening the stem and readjusting the headset, tightening the stem and the creak is gone! But not for long, after a few rides it came back. I readjusted again, and now it is back.
Not sure why it is coming back... Any ideas?