Shirleyaust

I am have vista home edition on my computer and built in microphone,
until recently my friend (in USA) and myself (in Australia) could have clear
conversations. Recently after about 10 minutes into the conversation at
the USA end which is a computer with XP, he gets an unbearable loud static
noise, necessitating him to have to turn his speakers down, whilst he
can still talk and I get a reasonably clear conversation from him, I have
taken up to typing my response due to the static. If we terminate the
conversation and I ask him for a new conversation, the static
remains...occasionally we can get a few minutes static free the second
time....what could be the problem