Some dvb boxes have their own volume control. (Mine does) maybe it is set too high. Check the instruction book and/or look on the remote. What is your TV volume control set at?
my tv was buzzing last night and it was the volume. tv volume was set far too high and i was using the dbox control for changing sound. leveled them both off to around middle and all fine now simple but effective!
If you have 2 scart sockets on your telly use the other one. My brother mentioned this noise to me today so i changed it to the other scart socket and its doesn't make any buzzing noise at all now.