Bad audio cable/connector maybe?
Both are provided by creative with gold pins, in further testing
I connected my main desktop to these speakers (earlier these were connected to my old computer) keeping everything same,
the hissing sound is gone completely, the main computer has branded SMPS zebronics platinum & also the sound card was different, my main doubt is now on old unbranded 400watt smps, cant fit the new smps in that old cabinet since its small old cabinet, will test later with the new smps & report back.
Speakers are now perfectly fine & I played upto 80% volume without a hint of hissing on the testing computer.
Any clue what else could be wrong , some kind of shielding required or insulation which may improve, when i connect the tv tuner with old set up i get a interference signal too see attached image which does indicate that there is some signal interference happening from the CPU/smps or some other source.
I need help to figure this out.