i started up my car earlier and out came this horrible noise, it lasted for like 10 secs then stopped! could it be a sign a belt needs changing as it only does it wen its been raining!
Yeah mate, your fan belt by the sounds of it.
as said above it can be tightened but sometimes it doesnt really help and a new belt is needed.
the reason it does it when its wet is because the rain acts as a lube and causes it to slip (makin the screaching noise-mainly on start up)