Thanks everyone.
Yes, I understand now that the FPS and the speed of the recording are two different things.
As Postman mentioned the drift here is small - I am not seeing a 0.1% speed difference that you would expect to see with a 23.976 / 24 fps mismatch. It is more like 0.02% or something like that.
Interesting point about the potential clock problems with the 5D - we are talking about a stills camera at the end of the day...
On a more general note, what is the usual workflow on a 24p project? I have just received a test video @ 23.976 fps - so I run my Pro Tools session @ 23.976 fps? At some point pic. editorial will need to do the change to 24 fps for the cinema release (DCP & 35mm prints are to be done), and I would prefer for them not to do the sound speed change...
How do people normally deal with this?
Thanks again in advance