All About the Games have discovered a fix for those of you with faulty whammy bars on your X-plorer controllers for Guitar Hero II. Of course Red Octane have already said that you can exchange your faulty guitar at the place of purchase, or send it in for exchange if it was purchased online, however AAtG say that this method doesn't void the warranty and only requires you to loosen some screws, so it may appeal to some of you as a quick fix.
First off, you need to place your X Plorer controller face down on a table or sturdy suface and remove all 11 of the black screws from the white body of the controller. You will need a long and thin posidrive screwdrive in order to do this.

Then once you've removed the back from the controller you need to locate the whammy bar's sensor mechanism.

The next step is to slightly loosen the two screws that hold the sensor in place and rotate the whole mechanism by only a slight fraction in a clockwise direction before tightening the two screws back up again, and replacing the white cover and tightening up the 11 screws again.

Get more details here at All About the Games