Try running your ground wire from the radios, directly to the engine block. It cured the alternator/distributor whine in my Cobra 148. And others said that they could hear a bad background noise in my transmissions as well, that is gone too.
The condenser that C5 posted, will work on the older vehicles, but although its possible, its hard to put on a newer style engine, since the distributor is made different.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...