ntl digital sound problems

my ntl digital box is connected to a bose lifestyle system by a standard 2 phono lead. i've started to notice that on certain news and sport channels (itv sport is particularly bad) the is a large ammount of interferance through the rear speakers. i would describe it as sounding like running water.

is this a problem with the broadcast or my set up (other channels i.e music and movies sound fine)?

have others noticed this and is there any solution?

 

My Arcam AVR200 has a 'ground lifting' switch to combat this problem. When set on ground there is background noise on NTL digital. When switched to 'ground lift' it disappears. I have no idea how this works but it solves the problem

Pip