Strange sound

[dl4002]

Ok so this sound started a few days ago, doesnt happen all the time, but is more likely to happen in the late evening.
Tried searching but have no idea how to classify the sound, its not a clicking sound, nor is it a beep. Ive uploaded a 20 second sound clip with the noise, may have to turn your speakers up

Any help is much appreciated

http://www.sendspace.com/file/bzsexw

 

[weaselman]

If it is a loud whirring sound, and vibration, it means one of the bearings in or copper bushes in the fan assembly is worn, So buy a new fan. Normally it happens most of the time when the fan is cold and starts up, and goes away once it is warm due to friction and heat built up.