I've been using the 4D quite a bit recently and there seems to be a bit of flicker when used at running pace? There's no problem when the 4D is used at walking pace, but at running pace, I don't know if it's something to do with the ND or shutter, but there seems to be a flicker that coincides with the footsteps? Has anyone else experienced this?

I've been using the 4D quite a bit recently and there seems to be a bit of flicker when used at running pace? There's no problem when the 4D is used at walking pace, but at running pace, I don't know if it's something to do with the ND or shutter, but there seems to be a flicker that coincides with the footsteps? Has anyone else experienced this?