Thank you, I had quite forgotten about about that!
However, I can select PF21 but cannot activate it, the "On / Off" is greyed out and wont select, am I being dense (as usual) or am I missing something?
As a Nikon user I only spent a few months with a 1D some years ago. If I remember right, you have to hook up the camera to the computer and activate the function by the Utility CD first ...
If the quiet mode isn't satisfactory, if you can lay your hands on a Camera Muzzle, it works great. I have one which I used on the D2X. Haven't tried it yet on the 1Ds.
even with it enabled it's still quite noisy and if your used to the way the mirror works in std mode getting used to quiet mode takes a while as the viewfinder blackout is noticeable. also it is only quiet in one shot mode not motor drive.
The 40d is v quiet in comparision, but not silent.