My vauxhall Astra makes a tapping sound from the top of the engine when I start the car?

it sounds like the car is due an oil change, you have hydraulic tappets (can followers)in this car and when the oil is thick and gummed up they will not work correctly. Change the oil and filter and refill with a good make of engine oil and make sure that you use the recommended grade of oil as this engine requires a thin oil.|||Have you chacked to see if the bonnet stay is secured?|||bad tappet, bad cam chain tension? If belt driven, prob bad tappet. If hydraulic lifters-try oil change with correct viscosity for weather. if not, adjust tappet(s) manually, use new rocker gasket unless it's rubber. else replace bad hydraulic lifter(s).|||Flush the engine before changing the oil and use an oil with a viscosity of 5w or lower.|||Bung a can of STP oil additive in!|||got oil in it?..if just a few seconds dont worry abt it|||that is not a good noise, but it probably goes away after a few seconds when oil pressure builds up. it may be time for a service and tune, hopefully that is all it needs. good luck