I'm not sure whether I should ask this question here but I'll give it a shot. I have a XT8 Dobsonian Reflector telescope and it works fine. But recently when I use the focuser to focus the image when I change eyepieces it focuses fine but it makes a scratching noise that is really loud and it doesn't sound right. Now I don't know what this screw that I am about to explain is neccesarly for because I am no where near a telescope expert. Next to the eyepiece there is a screw that you can turn loose and if you make it as tight as possible the focus knob won't focus the image but when it is a little loose it starts to focus it, but it keeps making a scratching sound and a high pitched rubbing sound that doesn't sound right. I know I explained this pretty vaguly but any help would be helpful! So far I could not find anything on the web for this weird problem.