[Hoagy]

hey all

i have a friend that let his fiesta run low (very) low on oil and developed from what i can make out a top end tapping. the car is a 96 model and the engine a 1.3 zetec engine. i have had both cam shafts out and inspected the hydraulic lifters which appear to be fine, when the engine is running the oil gets to them ok (now ive filled it), the strange thing is the tapping sometimes dissapears for a moment or so then comes back.
ive read this engine model had problems with sticking valves but i cant see this being the problem as it still fires on all for cylinders ok.

any idea's what could be causing the tapping?
any help would be appreciated.