Voice volume problem, please help!!?

Whenever I talk to one friend of mine on MSN, my voice volume automatically decreases, when he speaks, it's all fine with other friends, but with him, whenever he speaks, I see in my Realtek HD sound setting, and The recording volume gets decreases, I tried most of the settings in my PC, and I am sure, the problem is in his computer, I also told him to change settings, and he did, but no help. For sometime, it gets all fine,but after time, it gets reduced, He can hear whatever I play on speakers, even if I remove the wire of speakers, he can hear it out loud, but he cannot hear my voice...Please try to tell me what I can do to fix it, or what my friend can do? And, it's with all messenger, MSN, Yahoo, Skype, I uninstalled Skype too.. but no help..