I have just recently noticed that my Wharfedale Emerald center channel speaker is distorting when the sound peaks... kind of a rattling sound. I have all Wharfedale speakers in my surround system and the center channel speaker is the only one with this problem. Can it be that this speaker is already bad after only 18 months of use and only modest volume output (never above 1/2 of the receivers capacity), or could there be another culprit ? I rechecked all my connections and everything looks fine. I am not an expert on sound systems by any stretch, so I just want to rule out any other possibilities before I service or replace the Wharfedale speaker.