Does anyone else have this problem?

[Blair01]

I have a rebel XT and have stopped using the the auto focus feature on my lenses because the photos all seem too be slightly out of focus. I've noticed it's worse when I'm in the higher ISOs. Even when I manually focus if I go by the beep it will sometimes be slightly off but less often than with auto.....is there something that I could be doing that's causing this. I'm new to DSLRs

[SmartWombat]

ISO setting shouldn't affect focus.
But you're using the higher ISO when there's less light I guess.
Can you upload en example?
It might not be focus, but movement.