Is a Racing-Bike making creaking noises a sign of equipment damage? Last Sunday I noticed that my bike makes creaking noises (similar the hull of a ship, but on bicycle scale - imagine a rat making the sound "creak"). It seems to me that this is related to stressing the bike frame, but I can't generate the creaking in a ready manner, and sometimes it goes away. It also isn't connected to pedaling or bike movement. I can't pin-point a source(like a screw or bolt, or shaft). It sometimes creaks when I just get on it, then I can ride 10 minutes without a sound. Still, this is a new sound to me, and I've and I wouldn't want something in my frame to crack when I'm doing 50 down hill and going into a curve. I've gained 6kg since I bought the bike, might the extra weight be a problem? Should I worry, or has someone experienced something similar before?

All answers above were interesting - in the end I couldn't pinpoint the source of the creaking, but I gave my bike to a shop for a check-up, and they re-calibrated the spokes on both wheels, after which the creaking went away. No dirt or damage was be found.