I know it's impossible to diagnose without hearing an actual sound but, none the less, here are the symptoms described as best I can...

Car is running fine. No noticeable issues. 54 plate (2005) 4.4 V8 - pre-facelift etc. 118000 miles.

Except, once it's warmed up, creeping at just above tickover (not at tickover - has to be just above and I mean just a touch of the pedal) with the window open you can hear a knocking sound - it actually sounds like the noise you sometimes hear when they are pile-driving in the distance...

It doesn't do it in Park - only in Neutral, Drive or Reverse...

It doesn't do it all the time. Only when warm. Sounds sort of metalic. Speed changes with engine RPM - but as soon as you load the engine a little more it's gone. The sound appears to be coming from the rear of the engine/Front of the gearbox.- but hard to tell as I have to sit inside to make it make the sound!

It had the gearbox replaced/reconned at 80,000 miles.

Any thoughts? Torque converter about to die?

A bit more investigating later - and a black mark on my ear where I had a dirty piece of wood to act as a stethoscope...

Noise isn't gear dependant and is coming from front of right-hand cylinder head - Vanos unit I reckon. Perhaps an oil change will quieten it down - it's showing still 5500 till the next service, but an early oil change won't hurt!

Buy some cheap oil drain the sump and refill, bring up to temperature drain and refill with good quality oil and new filter

Twas exactly my thoughts.

I know it's got decent oil in there - because I put it in. Fully synth Mobil 0w40.

But it's done a good 12000 miles on it - all longish distance stuff though - I work 80 miles from home - so that's its normal run.

A drop of fresh wont hurt - looked inside the filler cap and it's all still sparkly clean...

Reading around the interwebs though - looks like it's not uncommon for them to make a noise... Let's hope that's all it does do.

Does sound like the Vanos.

As for oil changes, personally, I work to about 10k miles and change the filter and oil and reset the counter. I've found leaving it longer than that wrecks the paper filter. V8 or else ...

Cheers.

I'm still doing nearly a thousand a week, so oil changes are quite frequent!