Just curious if anyone can help with this?

I am using a **Canon 5D Mark II** and it seams to be having **noise issues** at ISO 250 and up and especially at ISO 400? What is going on?

In low light when my flash doesn't hit the subject very well it seems to be very extra grainy and also a bit blurry. Even when I am not in low light such as outside during the day and still using flash at say ISO 400 I still see noise? Once I am home and zoom in a bit it is so ridiculously grainy and not clear.

Any ideas about what may be causing this?