Odd click from SL EU3 engine

[wag]

My superlight EU3 began making a clicking noise whilst being driven gently. Noise was from the engine and revs dependent. I thought of valves and expense. When I got it home I listened to it with a screwdriver and traced it to the injectors. It then stopped and, at the same time, the tickover (which had been lumpy and hunting up to about 1700 rpm) became steady at 1000 rpm. I suppose I dont need to worry about it, but it is a puzzle