Sorry to bump and old thread, however I have a 2011 Cannondale Cadd8 that developed a bullfrog like creaking noise after about 500kms that I was certain was emitting from the bottom bracket. After servicing the bike and applying grease to every known thread and bearing + the skewers and the spoke contact points the creak still persisted. With the bike upside down i noticed a very small piece of sponge that was trapped between the frame and the plastic cable guide that is attached to the underside of the bottom bracket which must have been there since I last sponged it down. The creaking stopped as soon as I removed the small piece of sponge and I sprayed some lubricant behind the plastic guide for good measure. Thought it was worth mentioning as this would no doubt be a common place for dirt and grit from the road to be collected.