I highly recommend to you to open the case, reach the funs and clean them properly. Sometimes there is so much dust that it forms a small carpet that completely stops the airflow. Changing the thermal paste doesn't have a noticable impact, at least for me. I just did it before a couple of days and to be honest I haven't noticed any difference. On the other hand removing the dust has a huge impact. When I first opened my 2 Macbook Pro(s) before a year, they were both already 4 years old. The fans were getting noisy within 1-2 minutes of switching on: because of the dust. When I opened them, I was shocked by the amount of dust that there was in there. No wonder, they were so hot. At the time, I cleaned properly the dust and even put oil at the axis of each fan. Since then, it has been extremely quite and cool, better than new. Now, after a year, I decided to clean it again plus I put new thermal paste (I put Silver Arctic 5 last weekend). The paste doesn't make a difference, probably it doesn't worth the...