Stayed up late last night (early this morning) installing XM in my E. I ran 3 conductor 22 guage wire from the XM, under the floormat, up the side of the sub, and behind the AUX plug on the dash. Soldered 1/8" male plug on one end of the wire and used vampire taps to connect to the correct wires behind the AUX plug. Also used a jumper wire to short between the yellow and blue wires.

Setup works well enough but I get noticeable hiss whenever the XM is on and AUX is selected at the head unit. I've checked and the 1/8" plug is fuly seated so I wouldn't think it is a loose connection. Some suggestions I've gotten from neighbors (none of whom are stereo folks) are:

-Use an FM modulator instead of the AUX
-Put some magnets around the cable at various points
-Hook it up behind the factory radio instead of behind the AUX plug
-Get a better ground (ground loop something or other???)
-Use a connector other than a vampire tap to make the connection

In hindsight I probably should have run factory made wire for the connection but I already had lots of wire and the 1/8" plug at the house.

What can I do to eliminate the hiss?