Where is your antenna running? I know the DD has two C.F. tubes within the wing section. It is possible to pick up interference from the tubes, since they can capture RF signals. Be sure the antenna doesn't run parallel to the tubes...Are you using any type of metal to metal linkages on the setup. The RF they create can also be amplified by the tubes. From what I understand, some of the channels are more likely than others to suffer from this type of interference...Hope this helps. Dan