I've recently noticed a kind of creaking noise coming from, I think, the front end of my bicycle, though I'm not sure because it sometimes sounds like it is coming from the cranks. Maybe it's the wheels? What could be causing the creaking? I think all the parts are greased adequately. The frame is 4130 chromoly and I recently switched from drops to nitto RB-021 bullhorns.
Advice is appreciated.