New strange noise - possibly from fan?

[Yo Ma Ma]

Rather sporadic, but sounds just like a siren going off inside the case! Becoming more frequent lately it seems... think it's just a fan going bad?

 

[mechBgon]

Sounds like a sleeve-bearing fan has worn out on you. Can you spy out which one is the noisemaker? Sometimes they will do it only when they've been stopped for a while and cooled off, so you might shut it down, take the cover off, and let it sit for 20 minutes or so, then boot it up and see.

 

[sparkle]

It is definatley a fan, I had one that did the same a while back. If you tapped it, it would stop squealing.