My fan started getting noisy so I opened up my laptop and cleaned it out. I then put it all back together, turned it on and now it's even louder than before. The laptop itself is running fine, just that the fan is being extremely loud and running at 3000+rpm and the CPU is at 48-50 degrees celsius.
How loud a fan sounds is related to the friction within the bearing and how the vane is shaped to allow air to flow.
The above points to a fan's bearing wearing out. It may need a replacement.