most people dont open their pc very much
if you didnt for some years its a good idea to do some cleaning

see, your fan[s] tend to collect a lot of dust [ you'll be surprised ]

so????

open case
touch a water-pipe or something thats grounded
use a small soft brush to loosen dust [ carefull ]
use vacuum-cleaner with small tube or tip or something to remove the dust [ at low RPM ! ]

dont be funny to let the fan spin rapidly by the air-flow
it may damage the bearing !

thats it
happy hoovering
:dance2: