My Haibike has almost 2,000 miles on it. Recently it has developed an annoying creaking sound when I'm pushing down on the pedals (no noise when coasting). I have taken the pedals and cranks off the bike and checked them out - they're in perfect shape. The problem may be frame flexing. Has anyone else encountered this problem? Any suggested solutions other than 1) wear earplugs or 2) get a loud radio? Thanks in advance.