High air flow/ high RPM noise coming from my fan

Hello! I'm not very tech savvy when it comes to computer parts and what not. It's probably nothing, but the reason I'm concerned is cause my sisters computer (the same exact computer) doesn't have a loud fan.
My fan just makes a loud noise when I'm watching netflix, playing games and stuff.. Can anyone tell me why that is? I'm not stupid, I know it's probably because high air flow/ high RPM noise due to the fan spinning up in response to high CPU usage. I guess what I really wanna know is, how can I fix this? I appreciate any help! Thank you :)
 
Check the temps; this is usually the processor driving the cooling fan to MAX as it's getting too hot.
Open the system and clean out the dust!
 
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