I haven't had this issue with my 2 asus.. but on my bro's macbook he started facing the issue.
To fix it I made a tight vacuum seal on 1 vent and blew air in at high PSI (don't worry the fan will be fine, it is a brushless fan). I then did they same with the other vent. This way you get all the dust.
Best way to do it is to go to a mechanic shop, sometimes they'll let you use their pressure line for free