Having a problem With Easycap

Hi everyone

I've bough an easycap 2.1c from a site and installed the drivers and ulead.
Ive put the easycap on a rca cable(White yellow red) and connected the other end to my TV scart (backside).
With few changes ive got a perfect picture and a sound from the tv, but when i put a gaming console on the scart hole, i've got the Picture but no volume, Just some anoying BZZZZZZZZZZZZZZ.
i'm using Windows XP sp3 64-bit
and the consoles i've tried are Wii and Gamecube.

also i've tried to plug the game console straight to the easycap with the Wii's Own cable. that worked perfectly
Ive tought i need 2 pairs of Rca (Red white Yellow(or just one volume) and some Y-splitters for my video and volume.
Ofcourse i like your opinion and knowledge what is the problem.