high pitch ringing noise

[tf 85e3]

i have a mac 512ke that has a cooling fan on top when the computer runs for a bit it starts making the ringing noise and if i cover the hole where the fan blows air out i dont hear the noise.

 

[Phipli]

i have a mac 512ke that has a cooling fan on top when the computer runs for a bit it starts making the ringing noise and if i cover the hole where the fan blows air out i dont hear the noise.

Perhaps try dismantling and adding a drop of oil to the fan bearing. Only a small amount needed, the bearing is often accessible under a sticker on the fan hub.

 

[croissantking]

It could be the flyback as well.