I have a 48' exmark rider. What happend was when I took off the blades to sharpen then put them back in they all went in right except the one farthest from the grass eject side. I've tightened it as much as possible but there is about a 1/4 inch gap from being in all the way. I made sure I had all the spacers and everything was there. Nothing inside like dirt or bent steel pretuding it from coming in all the way. When I engage the mower it becomes loud then sounds normal again in quick frequent intervals. Any ideas?