I'd have to agree with
HerenIstarion. I believe that seeing how gollum only had a rag around his waist, he probably developed a cold, and therefor the noise he makes is probably his way of coughing. But there are a lot of other really good suggegstions. They were so good that I'd have to agree whit all of them, except
Imladris's idea (dont take this offensively please???) because Gollum only laughed when Frodo came into his life and probably before he left his village. But, again, a lot of the idea's are really good.
