Oka, so I am new to this whole cycling thing. I bought a new 05 Bianchi Virata from my LBS about 3 weeks ago. Other than the normal things, pumping my tires and cleaning/lubing everything I really havent done too much for my bike.
I rode about 17 times in the last 3 weeks with no problems. Including a 1h 45m ride around the city. Didn't notice any problems at all. Left the bike in the car over night and this afternoon (around 20 hours after I previously rode it) I got it out to ride. Did my pre-ride check of the brakes and everything and I seemed good to go. Got on the bike and started down the road easing into the ride. About 5 min after I started I planned on starting to hammer after I turned a corner at a stop sign... Well, when I got out of the saddle (kind of like I was climbing a hill) to get up to speed faster, I noticed a grinding/creaking noise every time I put pressure on the handle bars. I thought something was wrong and freaked out, put the bike into low gear and just lightly cruised home. When I got back I tried to figure it out and found out that just pushing down on the bike it makes the same noise. I can't exactly seem to figure out whether it is coming from my handle bars or something else.
PS. I am a n00b and did try to use the search function, but other than using sheldon brown and park tool I can't really figure it out...
Handlebar creak, they need to be tightened at the stem. The LBS will do that,just in case. You're going to have creaking when you put pressure. It was a very common problem years ago, actually MORE with HI-End bars and stems. I reckon because they're lighter. A minor creak could be impossible to get rid of, your's seems like it's very loose, not just a stress related creak.
If the bars and stem are alloy, ie not carbon, a very light coating of grease on the bar/stem joint will solve your problem. This is not uncommon for new bikes and the LBS should be able to do this without a problem.