WHat is this sound?

[Chris QTown]

Can anyone distinguish the metallic tapping sound that goes off in the background?
Im not sure what it is, but it sounds like metal on metal somewhere....
It goes off intermittently "ding......ding-ding......ding-ding-ding.... nothing.... ding..... etc....."

It started roughly 3 weeks ago...

http://img171.imageshack.us/i/ni1.mp4/

all feedback very welcome!

[BUSHWHACKER]

What happens to the noise when you rev the engine?

It sounds a bit like the harmonic balancer pulley is breaking up.

[Chris QTown]

it remains the same no matter what the revs are, which is a blessing i must say! it almost sounds like something on the outside of the engine is tapping but i cant find it. I heard the exact same noise on another diesel engine the other day, but it was a little lorry not a 4runner.

wont be able to find it anytime soon as my battery just died

[Albannach]

wont be able to find it anytime soon as my battery just died

rip