@Sara8 white static on a digital device would normally indicate a local issue, possibly interference from another device or even a bad connection with your TV input or hdmi lead.
You haven't stated which NowTV device you have or if it's happening on other apps from the same device but if it is a stick, try removing it and putting it into a different hdmi port if you have one spare. If it's a box, try a different lead.
Also ensure there are no other electronic devices near by and leads behind the TV are free to hang and not all jumbled up.
Thanks for laying some useful knowledge on me, you see I always thought that "white noise or static" on a small device was an indication that the device was going wrong, not interference.
But now, with that knowledge, I now know the action I need to take with my own digital devices.