I have a set of 2005.1 Kef eggs connected to a Denon 3802 amp. Recently the eggs have started to emit a high pitched tone which, although not loud, is noticeable whether playing a source or not. The tone only disappears when I disconnect the subwoofer but then I don't have any bass. I'm not sure if this is a problem with the amp or the subwoofer. Can anyone provide any advice?