I had same issue and I fixed it this way:
1. I opened the computer and removed parts until I had removed the speaker bar. I stopped here because I didn't wanna break anything and the next step was to remove the display.
2. Cleaned the fan with compressed air bought for 10 $ because it has a long pipe so you can get into the fan. A lot of dust was removed!
3. Putted it all together again.
4. Now it works fantastic! Two years of dust is gone