Originally Posted by antsjeep
Check the location of the ground. Make sure it's tight and making good clean contact to bare metal. If it were my jeep id run a single 4 gauge ground wire directly from the battery into a distribution block to ground anything your installing that's aftermarket.
If not, you can always just use an existing bolt (seat belt, seat, etc..) Basically any point that is connected to the frame.
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Both power leads can pick up either radiated or conducted noise.
Radiated would come from running a long +12 or ground too near a noise source.
Conducted from picking a poor power or ground tap.
Most modern alternators aren't that noisy, but you'd need an o-scope to check them as if the cables to the battery and frame are well cleaned and tight, that tends to cut engine speed related noise.
If you had a shop install this, pay them a nice visit, as although your unit may have an internal filter, they should have equipment to tell if the noise is coming from the power/ground feed or is being radiated into the unit.
Conducted noise is trivial to get rid of, usually with a capacitor pair where the two are wired in parallel with a small higher frequency one and a slightly larger lower frequency one. Adding inductors should be avoided if possible as they can limit power.
Radiated noise is also easy as copper mesh is cheap, but making sure it covers the issue isn't for amateurs.