Background: I have a '96 Civic, and I installed a portable XM radio device several months ago. It’s powered through the cigarette lighter socket, and connects to my head unit with an auxilary cable.
When using it, there’s the most mind-numbingly annoying background noise: sort of a high pitched-whine that varies when I accelerate or increase the electrical load (turn on headlights, use the power windows, etc.) I noticed that it was less prominent when I switched to a different power adapter.
I just got a Myfi (joy!) for Christmas and I hooked it up to my car in a similar matter. The sound is still there, but (since the Myfi can run on its own battery) I noticed that it disappears entirely when I unplug the power adapter.
Now for the questions: How can I get rid of the sound?! Why does it exist at all? Shoddy XM radio design? Is there a power filter of some sort for cigeratte adapters?
The head unit is aftermarket, and the factory stereo power wiring was altered for my previous head unit (which didn’t have aux input) - I just used the same power connecter for my new one. Could that somehow be at fault?
There are a few different approaches to getting rid of this noise, such as rerouting your signal cables to be farther from power cables, installing capacitors that buffer the power source, etc, but I don’t actually have any experience with them. The only reason I’m posting to this thread is to tell you that what you have is commonly known to car stereo installers/enthusiasts as “engine noise”. Hopefully that helps you in your google searching.
After fooling around some more, I should probably post a few more facts:
-The sound is worse when the MyFi is off
-The sound still occurs when the ENGINE is off (?!) with the key at the first notch
If I can’t find any solutions here or on Google, I’ll probably end up taking it in to an audio shop (anyone have experience with Tweeter in this regard?).
Ok, it’s almost certainly some sort of noise on the power line, from what I can tell. Get yourself a couple snap-on ferrite cable chokes - available at fine electronics and audio shops everywhere. Put them on the power cord as close to the XM unit as possible. To increase the inductive filtering, you can loop the cord through them a few times, if necessary. If you’re lucky, one choke is enough, but if not you can add a second or even a third, although I doubt you’ll need that many.
