[mdoyle]

I don't think this is usually alternator related, it's more likely due to the HV in the ignition system from a partial failure. You'll see the same effect if you ever run non-shielded spark plug cables, and it's the same reason Corvettes used metal shielding boxes over their alternators (no metal body panels to shield RF).

The alternator is putting A/C through a diode trio into D/C, then a rectifier so you'd need a pretty messed up component to cause radio interference in that circuit.