Ruwan,
Pls answer these mate coz other wise i cant help u out.
Where have you taken your power from? Is it from the ignition or some other mean like power from the cigaratte lighter..etc?
Is ur vehicle diesel or petrol?
Also how old is ur vehicle. Has it got a ECU? (If u dont know.. tell me the make and the model of ur vehicle.)
Noise..
its not only alternator and spark noise, but often also EMR from the engine management system.
cheers..!