Used to have that problem with my freeview box, try flicking through all the different AV channels i.e AV1,AV2 or EXT1,EXT2 until you cant hear it. Or if there is more than one scart hole on the TV try changing the one the xbox goes into
I will try the different scart hole if my tv has one, thanks. But i cant play my xbox on a different channel as it doesn't work on any of them and i dont know how to make it work on them???