Mine does it when its cold. It's definitely a belt issue. During the summer it rarely makes the noise unless, like in your case , it rains alot. It never got bad enough for me to worry about though. I can tell you one thing though.... I used belt conditioner and it gummed up everything and make things worse. I tried to clean all of the "sticky" off of my pulleys and bought another belt
. I won't use it again. Let us know what you find out. Thanks for the post. T.