Rose, remove the side the panel and determine which fan(s) the noise is emitting from. First step is determining if its cpu or case fans. My guess is rear case fan if pressure stops it. Dust build-up ...

I have a 80mm Sunon monuted on the top of my case pulling air up and after a couple of weeks it started making a pulsing, mettalic vibrating sound. Really irritating. I've tried to mount it as tight ...