You could try going into the custom function menu and seeing if the noise reduction is on or off. Select on and see if this helps the muddines. It does have an impact (under certain conditions), on write times (to the CF card), but would affect this more when you shoot RAW.

There are other software products such as Noise Ninja that might also help you (I have not used these myself yet though!).

Noise reduction on or off shouldn’t be making a great deal of difference at 100ISO in (Even poor) daylight.
The other custom functions need checking too. Set them all to default until we solve this problem.