tap tap

I have an m reg 820 it has of late developed a tap tap noise on tick over its about every second and speeds up as you open the throttle is this a dodgy tappet it seems to originate from that sort of area.does it need to be sorted or is it one of those rover type problems that you live with 'cos it to damn expensive to repair. *"!?ing car always going wrong id be rich if her indoors would let me sell it,I tried to sell it once no-one wanted it,you cant give 'em away!!!!! sorry bad day any help would be appreciated thanks john