I thought there might be some of you fellow PS4 owners like myself who may be searching on how to fix this.
I have a day one PS4. So for the longest I was having a problem with my PS4 sounding like a blow dryer and didn't know why. Everytime I played a game the fan would kick on immediately and it was so loud I would usually put my headset on while playing to drown out the noise. Not to mention the PS4 would heat up my room like a portable heater. I honestly thought I had a defective PS4 and just accepted it as I was a day one adopter.
After awhile though, I just couldn't take it anymore so I began researching if there was something wrong with my PS4. I kept my console pretty clean (dust it, well ventilated area, air filter in room) and didn't think of it being a dust problem as the issue started to occur not too long after I got my PS4 (I remember it got real bad when Dragon Age: Inquisition came out and I would play it).
Boy was I wrong about thinking it wasn't a dust issue.
Following the steps from this article on how to fix your loud PS4 solved my problem completely! I 'm happy to say I haven't had the issue since. Just be warned that this method will void your manufacturer's warranty but I didn't mind because mine ran out.
Hope this helps others because I looked all over the internet and people kept asking about the problem but there weren't many solutions to be found.
Edit: Moved from General. - space_paranoids