Top end tapping

Question

hi,my name is ed.from cape breton n.s.bought my son a 250cc 4 stroke dirt bike from giovanni.it was brand new when i got it and i was wondering if the valves have to be adjusted after so many hours of using it.there is a tapping noise coming out of it and it sounds like valves to me but i am no mechanic.sounds like it's in the top end.power and reliability seem to still be there though.any help would be great thankyou.