ok i noticed this problem about 4 months ago but it just recently started getting worse about a week a ago. i thought that the sound was coming from the valves so i got my valves adjusted but it sounds like the tapping is coming from either the belt tensioner or the water pump. the strange thing is that it will only start tapping when the engine is warmed up, and it also sound like if one of the belts is rubbing on something. it only does both of these things when my engine is warmed up.