VW Passat B6 2.0 TDi Estate - Constant ticking/ clicking noise 56-reg Passat B6 - drunkenoaf

Has anyone ever come across this before? The car ticks, 24/7, like a bomb's about to go off.

It's coming from the engine compartment, I think, in the bit in front of the (UK) Driver's steering wheel. Very odd. Think it's electrical -- but don't have any idea what it is, and Google fails to inform me?

Hopefully that car won't explode, but after 134,000 miles and its reliability history...

http://www.youtube.com/ watch?v=rYAzen2pQc0