squelching sound and bad reception on ntl cable channels

[tatu]

hi,
some of my cable channels are making a squelching sound and picture is coming on and off,,,wost of my channels work ok but i have a good few like this such as living and bravo which i cannot view at all...ive rebooted a few times this week and sometimes it takes the channels 1-2 hrs to come on screen again...weird!! but most times it reboots ok and within 2-3 mins the cahnnels are up and running again exept for bravo living ones that have this picture/squelching sound...any ideas wot it could be? maybe the scart? i dont know....thanx