new a850 glitching on sd and hd channels

hi, got a new 850 this week with the attenutor fix already applied.

however, i've noticed the following:

- standard definition channels glitch periodically, square blocky pattern effect
- hd channels glitch less frequently than the sd channels but producing a weird pattern affect which i thought was fixed by the psu mod?

firmware is up to date.

i had an a780 before and had no problems with glitching apart from the odd occasion here and there.

any ideas what may be causing this?