If you've been cranking out some serious riffs on your Guitar Hero II controller, but have been noticing a few glitches with the ole whammy bar, chances are you've got yourself a malfunctioning unit. According to Red Octane, the bar on Xbox 360 axes could have a "calibration issue that may stem from a feature put in place to ensure accurate scoring." The duo of units in question sport 95065 and 95055 model numbers, but according to various user reports, even boxes with model numbers outside of the two aforementioned figures are on the fritz, too. Thankfully, it appears that Red Octane is working overtime to figure out (and solve) the quirks, but for those who'd rather return their current unit and try out another, that appears to be your prerogative. Be sure to hit the links below for a bit more info, and make sure you find other ways to exercise those phalanges whilst waiting for a return unit if you plan on staying in shape.
P.S. -If you're brave enough to want to try the repair yourself, there's already a guide. All hail the internets.