of detail here but from my experience, the only way to fix that is a new fan. If it's the processor cooling fan you better be doing that post haste before you fry the cpu .
For now I'd be leaving that cover off so I could keep an eye on things.
Pay small now or pay big later...
My fan makes this grinding noise lately. I've had this a long time ago, but I fixed it somehow by pressing on the middle part. There was a click and it was all fixed. Now when I touch the fan a bit the noise disappears and I won't hear it again until the next boot. For now I'm basically removing the panel of my PC every time I startup to fix that noise. Does anyone know what to do with this?