Mystery Noice

[Deanna]

I purchased a new Trek 2200 about 3 months ago, and there is a noise I cannot figure out coming from the front of the bike. It sounds similar to creaky floorboards. It's especially loud when I'm standing to get up a hill. The really strange thing is the noises are especially noticeable when it's warmer out--almost no noise in the morning and then lots of creaking in the afternoon.

I've made sure everything is tightened down and well lubed and it's still there. Does anybody have any idea what this is? The bike is a combination of aluminum and carbon--could those two materials be rubbing weird?

Any clues would be appreciated!