My 3802 seems to have some interference. When any input is selected, there is a slight hissing from the tweeter. The volume of this increases slightly if main volume is increased. If an input on the multi selector is chosen, then it can be heard in the hissing. What have I done wrong, or do I have a faulty unit? Setup is 3802, Marantz CC4000 CD via Straightwire coaxial, Mission M74 mains and M7C1 centre. DVD and the rest of the speakers/sub to come... Thanks all. David.