Hey Rebbie!
You could also try to stop your
CPU fan, by disconnecting it, or stopping it with your finger.
But, only do this if you know what you're doing and don't do it for longer than a few seconds.
If the sound stops when you stop the fan, it's clear that this fan is making the noise.
Again, be careful, if you're not sure on what you're doing, don't do it.
Blue