Discussion
are you sure its coming from the engine(internal)may be worth checking exhaust manifolds for blowing where they meet cylinder heads,produces similar sound,if you get a length of hose 1/2 inch approx diameter,hold this to your hear(stefoscope) as you probe around exhaust as it exits cylinder heads you are looking for a clack,clack sound where the gases are escaping from joints,dont hold hosing to near hot exhaust for obvious reasons.failing that it may be cam trouble looming,when did you last change oil & filter you may just have sticky tappet/s clean oil as a habit of getting them working properly again.
Edited by that daddy on Thursday 7th September 15:55
I had a tapping noise last month but that increased with revs. There are a few theories on this thread, unfortunately it happened to be the most costly one. Oh Well 
www.pistonheads.com/gassing/topic.asp?h=0&t=295878
www.pistonheads.com/gassing/topic.asp?h=0&t=295878
mm33 said:
bga said:
How loud is the tapping? Does it sound like metal striking metal?
Does the frequency of the tapping increase with engine revs?
Does the frequency of the tapping increase with engine revs?
Frequency does not increase with engine revs
Forgive me for this stupid question - but is the noise present while the car is not moving and if not is it speed related?
I had a tapping noise from the drivers side of the engine. Turned out to be the cover over the fan belt, where it goes around the alternator, rattling off the exhaust manifold. Sounded very mechanical, exhaust must have been acting a bit like a drum and increasing the noise. Easy fix though 
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