I think I'd find that not very pleasant to be sat there then a rooster crows every so often, I've never heard of that before lol. Famous and borat could be onto something though.
hmm you know i think famous is right. it could be aim. i used to hear a really annoying burping sound and eventually found out how to fix it. (turn off the sounds in aim)
id say it is either spyware/adware or a website advert. i get smiley central and other crappy ones that speak all the time. run hijack this and spybot s and d and see what happens. i suppose it could also be some dogey installed program. check in the startup list