Strange Sound

[Qualudia101@aol.com]

At exactly about 3500 RPM my engine makes a sort of "ting" sound. It goes
away on either side of this RPM. The strange thing is it only does it if the
lights or air conditioning is on. Like as if this is related to voltage drop
in some way. No difference in performance though. Thinking it might be the
ping of beginning knock,I have tried retarding the ignition to almost "5deg."
advance, also used racing fuel,but no difference. Keep the lights off or air
then no sound.....what gives .....anyone know?

Frank 93 SE-R