I’ve a T100. When I try to start it, it has a loud metallic click in the valve area. Like the valve is sticking and then popping closed. It’s been parked for a while. It has 600 miles on it. I got it from the PO just this last week. I’ve changed the oil and filter and added top end oil to fuel. Any ideas? It’s on the left rear valve of the engine (ref sitting on it). Thanks in advance for any help.