Er, right. Well, it's sort of egg on face time. I have finally seen what you chaps are on about.
For the last four weeks my CFV-39 back has been away being fixed under warranty, so I was working on LR3 b2 with my existing landscape shots. I just got the CFV returned to me today, and managed to get out this afternoon to take some test shots.
It turns out that I couldn't see this noise thing because my existing shots just didn't show it up - trees and fields and stuff full of intricate detail just don't, apparently. What it seems to need is a smooth area of white or pale colour in just the right amount of partial shade - like a window frame, in this case. And bingo, there was not only colour noise but yes - a sort of speckly texture a bit like porridge which shouldn't have been there. Luminance noise, at last. So I proceeded to attack this tiny section of the picture in LR2, and got it fairly well smoothed out. Then I pulled it into LR3, converted it to PV 2010, and had another bash. And yes, LR3 does a much better job, so you are all correct, and at last I know I am not entirely blind, stupid or mad. Which is quite a relief, really. Interestingly, though, of the six test shots I took around the cottage and garden, only this one showed luminance noise (that I could detect).
John