Just recently, the GCV160 on my mower started making clanking sounds, like 5 or 6 "clanks", when it powers down. When it is running at around 3100 RPM, it sounds fine. Took shroud off and spun the engine with a drill .. sounded fine, no clanking. So, when doing that, nothing is interfering with the spinning nor shut down of the engine. Blade is balanced & not hitting anything. Tried another known working recoil (in order to rule that out) & still clanks. Don't know that this noise, though worrisome, is actually harmful. Any ideas?