I have my ipod and Sirius right next to eachother, that way I can easily swap the 3mm jack from one to the other. I have had this setup in both my previous vehicles with no problems.
In the ranger, the 3mm jack is ran from the Aux input on the front of the HU, behind the dash, under the cupholders, and out to the units. After a few minutes of listing to the Ipod, there was some NASTY interferance, some pretty ear shattering noises. With the jack plugged into the sirius, it is fine. I don't even know where to start here, any ideas?