Tapping Engine

hello people
i have a mk2 golf gti and it i have just recently changed the head gasket timed it all up and is running fine. however it has started making a tapping sound, tractor like. now the oil light is coming on and i have tried changing the sensors this was prior to the tapping sound.now im assuming that its the oil pick up? what are the chances of it being this?  could it be anything else

could be thats there is no oil getting to the head sounds like the buckets on top of the valves are being starved of oil hence the rattling tractor noise

changes oil pump in sump and fixed problemo!!!