I've got a set of these speakers which I bought new about six years ago. Recently I've noticed an occassional buzz/vibration from one of them in the loud parts of movies. Removing the speaker cover seemed to fix it but I couldn't see that the cover was fitting any differently to any of the other covers. I swapped the cover with another one and the problem is still there. I have now noticed it to a lesser extent when the cover is removed. Is this a sign the speaker is on its way out? If so would the cover affect it like this? Should I try removing the speaker from the cabinet and swapping it with the one on the other side of the room to see if the problem moves? (Is this easy to do?) Thanks for any help.