I have a 95 GXE not sure on the engine size I'll check and add if needed. I have the stock radio. After a tune up of plugs, wires cap rotor and a alternator in the same week. I noticed the alternator wine on the radio. It so bad that if I had a hand held radio near the car you will hear it there as well.

get new plug wires.
dont get cheap ones, use either genuine nissan from a dealership or use NGK wires.