Why is my laptop fan so loud

my sisters laptop's fan is so loud every time she uses it. i just recently looked at it and there are some problems ive found. first of all she had some programs that were installed that constantly had pop ups asking to buy and download shit. not sure if they were viruses but ive already uninstalled them. another problem is that she is using windows 7 and its not a genuine copy.

main issue is the fan. like i already said my sisters laptop has many problems but i have no clue whats causing the fan to be so loud. the laptop isnt even overheating. it would only take 5 minutes after i log in and the thing starts making that annoyingly loud fan noise. if anyone has any clue what i can do to try and fix it, please tell me. this is most likely something my sister has done and i hope its something that can be fixed.

 

replacement fans are easy to find on the internet. If you feel comfortable taking apart a laptop, you can see what size the fan is, and search around for a replacement fan.

 

I had a similar problem with a laptop and the answer was to raise the rear of the laptop.

when it is standing on a desk or table the air intake is restricted so just raise the rear by putting a book or something that raises it about 1 inch at the rear and this gives a better airflow.

Another problem could be dust and fluff in the laptop if it has been used for a while.