Ticking noise

At the rear right, where the fuel tank filler is. When I turn the igntion to acc or on, and when the car is running, there is a 'clack clack clack clack' noise. It sounds like a tapping noise, and it's constant and consistent. Pretty much as soon as the key gets into 'acc', it's there.

Now, a few days ago I turned the key and the noise stopped. And then the engine would barely start, it was like there was air in the fuel system.

Now obviously that noise isn't right, but what the hell is it? Obviously the TD27 doesn't use a fuel pump, but if it did, that'd be the problem.

In the Terrano, for some unknown reason, the auto trans computer and glow plug timer are in the rear quarters. I guess copper was cheap back then. Anyway the only explanation I can possibly think of right now is that the glow plug timer is clicking away with some sort of problem and it's not glowing the plugs, hence the hard starting.

One way to confirm it is to jump the glow relay under the bonnet with 12V straight off the battery for 10 seconds, and try starting.

Well actually, the glow plugs get warm fairly quickly. It has normally only happened when I'm low on fuel (like, the last 3 litres, coz I live life on the edge), or I've just filled up. So normally the engine has been running well. It happened once whilst driving to Warby, I'd been in the car for about an hour when the thing just started shaking and stalling. Turned it off and on whilst rolling down a hill a few times and it was jumping back and forth, eventually it kicked over and started again. It's only really happened about 3-4 times in the past month.

There also seems to be a huge build up of oil/grease/slimy black crap in the rear quarter near the fuel filler along the fuel pipe etc. It's pretty disgusting. Almost like there is a fuel leak?