XM RoadyXT static

I have a 08 Prius with Package 4 that I picked up last weekend and I love it. I have one annoyance that is driving me a little crazy.

I put my XM Roady into the Prius and connected it to the Aux Input. I'm using the same cabling that was in the old car. I'm getting a ton of high end hiss from the unit that I didn't get in my previous car. I have to turn the treble all the way down to be able to tolerate listening to the XM unit.

The Roady is plugged into the cigarette lighter in next to the aux input if that helps.

Any clues are appreciated...

Matt