Sound Issue

Recently my PC has started to put out a very loud and annoying static sound when connected to my TV, at present i use an DVI-AGP converter as my TV doesn't support DVI and a standard 3.5mm jack to jack input from my PC to my TV for sound (I do have the cable to do DVI-HDMI and Phono sound but I've tried and tried and tried but just cant get them working), Does anyone know how i can fix this sound problem as it interrupts watching DVD's, Listening to music, Gaming and just general browsing because it is that loud,

Also if anyone knows how to set up things with my other cables and can explain it to me that would be much appreciated,

The TV i have is a Samsung one (the one they showcased the Xbox 360 on in games stores, don't know model number), I have an on-board sound card (MB = P5Q Pro) and my GPU is a BFG 260GTX

Hope someone can help
7,