Ahh... the famous tapping sound. Okay at this point I would do an
experiment. I would change the oil to synthetic 5W40 and drive it around.
First couple of hours would sounds like it is so much worse... but then
afterward. it should quieten down... engine will run much smoother.
If the tapping doesn't go away, then you got a different problem... which is
wear and tear of the camshaft. This is easily checked by pulling the valve
The reason for synthetic is that the oil channels to the hydraulic lifters
may be clogged by regular oil coking and by running synthetic, you can clean
it out somewhat but the oil flow to the lifter is much improved thereby
closing up the gap that cause the tapping noise.