hmmm it could be a fan yes... or it could be a hard drive problem... when hard drives are on the way out they can whine and knock sometimes.
heres a quick test for you....
HARD DRIVE DIAGNOSTIC LINK
Data Lifeguard Diagnostic for Windows
File Name:
WinDLG.zip
File Size:
4.25 MB
The link above will take you to the download page...
download this APP install it... when you run it it should give you a tick if your hard drive is healthy or a cross if its on its way out.
this app reads the S.M.A.R.T info from your hard drive which can show you any faults that are happening to your hard drive - click the small notepad icon to read all the S.M.A.R.T. info and see if theres any crosses there...
if there is it means your hard drive is failing and it could well be time to get your data off it and onto another hard drive... ive learnt the hard way and lost about 4 drives now - they just die and never turn on again sometimes.
feel free to do the quick test and extended test for even more info
DO NOT RUN THE WRITE ZEROS TEST!! IT WILL WIPE YOUR HARD DRIVE WITH ZEROS!! leaving you with no data.....
its safe to use the rest and can give you a bit of insight to how long your drive will last.
If your hard drive passed all tests then i would say its a fan!
again - fans clog up with furry dust and can congest into heatsinks and block airflow - the dust can even burn/scorch so every once in a while get a cotton bud to clean the fan fins and use a coctail stick to unblock trapped dust bungles in the heatsink fins... you pc will love your for it
clean case fan, CPU fan and heatsink and also check graphics card fan if it has one....
it will help keep temeperatures down aswell as noise
(piss easy too)