Squeaking aux belt

[Chrisjk]

Does it just need tightening?

 

[Mark One]

make sure it's not too tight otherwise the pulley bearings will go.

As a rough guide, you should be able to twist a fairly long stretch of the belt 90degrees and no further.
If it's due, change it. If you CBA, belt slip

 

[Chrisjk]

It was changed 3/4 months back and only recently started making a little noise as the temp has dropped.