Mate drove around his 1.6 16v astra that has a nasty top side tapping sound.
I have spent a good hour going around the engine and have not located where it comes from.
It does not burn oil nor does it breath heavy, does not over heat and has oil pressure.
spark plugs look clean and has no idle or starting problems, the power range seems fine and it is quite responsive, no hesitancy on acceleration either.
in other words it drives really well other than a nasty sound.
I have gone around the engine with my hand to find the noise in terms of vibration and knocking and believe it or not the inlet manifold area is the loudest part of the engine and also I can feel the knocking from underneath the manifold nxt to the inlet ports
I done some research and found that the inlet manifold has swirl flaps ?