I've just been underneith the car for another good period trying to work out what's going on....
I can now confirm this is NOT an engine issue. Engine is sweet as a sweet thing that's not sour.
The closest winner is..........
....... Kevin Wood

The noise is definitely coming from the transmission area.
I had the advantage of someone to gently rev the engine, while I was underneith, this was a great help in identifying what was up. It's definitely coming from the bellhousing / Torque converter area.
I popped out the two rubber bungs, one under the bellhousing, and one in front of it. I checked all 6 bolts holding the TC to the driveplate were secure - which they are.
So I'm with Kevin - either, a foreign object in that area... or... torque converter failing internally?
with the bungs out, I moved the engine slowly around a few revs by hand, closely watching the flex plate and TC as it came round. Nothing seemed out of the ordinary..
I have also noticed that the noise is only present in "Neutral" or "Park". When in any gear, incl reverse, the noise is not present.....
If foreigin object... how would that get in there, given both bungs are in place?
