Need Help with my sound i think

Well guys I've been having this problem for 2 months now. The problem is that every time I connect to ventrilo i can't hear some people. I mean that to some people in ventrilo I just hear noise when they talk. The funny thing is that, this happens to only few people not all. I can hear other perfectly. Example: "Sin" I can hear him so good but I don't know if I remember correctly "Final" or "Guntrix" I don't know which every time they start talking i hear only noise and I have no idea why. I've been trying to look on Ventrilo forums but nothing. PLEASE TRY TO HELP ME. -blue (sorry for my bad English)