I've recently added a center channel (7.4) to my BeoSystem 1 in the living room.  Previously I was simply using my lab 3's and BL2.  Since adding the center channel there is a popping noise every time I change channels, sources or the DVD changes to another track or menu.  At first I was thinking that the BS1 may be switching between Audio 2 and 3 mode but now I'm not so sure.  Never noticed it before adding the new speaker but it seems to come from the stereo speakers as well.  Could this be normal on this older analog system or is it a sign of something amis?