Okay, so I have a KHT1000 AV system but with it's small Uni-Qs is great for my tiny lounge. I have used it for 4 years now but last week, I turned on the amp then the sub (always off) and got a very loud low sustained bass noise from the sub driver. Bad connection? tried that to now avail. Took the board down to KEF and had it tested. Nothing wrong but complimentary replacement bits "just in case" - when home, reconnected the line-in and the same noise! And I mean LOUD. No volume or phase changing affects it. Not a whiz at electronics guy so please help with a dash of dumb for me?