Good Saturday Morning

[Cleo]

I've seen many displays over the years have their florescent tubes go bad. I even replaced them myself on a laptop that I had many years ago. It's rumored that Apple is working on LCDs that use LEDS for backlights instead of florescent tubes just for this reason.

Sounds like the fan in your Mac mini is going bad. Very easy to replace and cheap too but you do want to replace it before it stops working all together and you Mac mini overheats.