Mower about five yrs old. At low idle had a interal noise after raise throttle noise disappeared. Yesterday while cutting son noticed engine nosie and cut mower off. I listen after a restart, sounded like something came loose. Pulled engine open. All looked fine. Piston arms good. I couldn't see any reason for "knock". Any suggestions?
You didn't give us much to go on, like type of engine and model numbers, which would help us help you. From the little you did stay, I would start by looking at the overhead valve clearance. It should be adjusted every 3-4 years depending on use.
