Ok, so I have been having a problem with my XM radio in my car. I bought and aftermarket headunit with the 3.5mm aux input jack in the back so I could plug in my iPod. Well, my portable XM radio (Skyfi 2) also has the 3.5mm output jack. So I decided that using this direct input would be better than using the built in FM transmitter (due to better signal quality, and not having to reset the radio frequency when driving through different areas due to interference). However, when I use the direct output (3.5mm jack) of the XM radio, I was getting a hissing/buzzing background noise. But with the iPod I was not. So I discovered that the iPod worked perfectly without the noise since it was running off it's own poer source (internal battery) whereas the XM radio draws its power from the cigarette lighter outlet. Research revealed that this is where the problem lies. The car power outlets do not have an in-line noise reducer so the noise was being caused by a ground loop from the power outlet. But I found the product that fixes it quickly and easily. Here is the link
http://www.crutchfield.com/S-Mfcfe8N...+loop+isolator So, in summary if anyone else is experiencing this background noise when using the direct (3.5mm) output of an XM/Sirius radio, it is caused by a ground loop and you have two options: 1) Get the ground loop isolator from crutchfield that I linked to 2) Figure out the maximum amperage of power you will ever draw from you vehicle power outlet and get/install a corresponding inline noise-isolator/supressor (could probably get from bomb-shack) The first option is much easier. With the second option, you will have to expose the wiring to your power outlet, and then cut it and install the noise-supressor behind the outlet and probably have to run another ground wire. Option 1 is also only $18 and it has a built in signal booster to avoid losing sound quality when the unwanted loop frequency is stripped from the output signal. They also have one available with the RCA connectors if your head unit does not have the 3.5mm input (dealers refer to as "iPod ready") With the one I linked to, just make sure you install it the right way. One cable is the output (leading to your head-unit) and the other end is the input (leading from your XM/Sirius 3.5mm jack) in my case, I had to get some adaptors to convert the male end of the cable to female and the female end to male so that it would be hooked up in the RIGHT DIRECTION. If you accidentally hook it up the wrong way, the annoying noise you had before will be still be gone, but the signal booster will not function properly and the sound quality will not be as good as if you had done it right. I really hope XM/Sirius start installing some type of noise-supressor/ground loop isolator in their future radio models so that this addition will no longer be neccessary.
Fix for those using XM/Sirius Radio 
