If the problem is not the sandpaper itself it might be a faulty dust seal/ break. This component not only keeps dust out of the motor but regulates the speed of orbit. One easy way to tell if this is the problem is by listening to the sander when it is off of a surface. If it seems to get louder than usual when off of a surface it may be time to change the dust seal/ break. This is a simple replacement and the steps to do so can be found here [guide|62060] .