Yesterday morning climbed to el Portell de Valldaura hearing again a little annoying noise that seemed to come from the bottom bracket. To make things even more baffling I remember having swapped the old cartridge for a fresh one not so long ago (three or four days, may be?) and, after a careful inspection, it didn't looked like coming loose. Thus, in a mood of empirical enquire I started to check the bike while riding and observed that the noise appeared when hitting hard on the left crank. I gladly assumed it just was the pedal axle asking for some grease but when I dismounted for a final confirmation it appeared to run smoothly. I was puzzled. Perhaps the frame had developed a crack? (cold sweat). No , I inspected it carefully last week (sigh of relief). Then, all of a sudden, when I was giving way to despair I accidentally touched the rear fender and... it sounded much like that intriguing noise. The final diagnose was simple: every time the frame flexed under my powerful (ehem) left stroke, the left chainstay touched the rear fender causing to vibrate. After a skillful field repair (squeezed up that bit of the fender) I retrieved my peace of mind. Now everything seems ready for next Sunday (but for the rider).