Need Electronics advice/info

I'm tired of getting Noise on my CB and AM radio in all my vehicles.  The
noise is coming from the engine, but I'm not sure (yet) if it's from the
ignition system or the alternator.  I have supressor spark wires and
(maybe) cap and rotor.

What works?  Before I start buying "noise suppressors" from Radio Shack et
al. can anyone give me a primer on what I need to do?  Specifially, is it
more likely that the noise is coming through the power wire, or via the
antenna(s)?

Thanks for any help.

James