PCI Fan speed acting strangely

[fatespawn]

I recently removed my old GT120 and added an RX580 Sapphire Pulse to my system in anticipation of upgrading to Mojave. I'm still running 10.13.6. Everything is working as expected except for the system PCIe fan. Normally, my fans idle <1000. Low enough they aren't too audible. Well, since installing the RX580, the PCI fan always runs at about 2000RPM and is noticeably loud. At first I chalked it up to less airflow and more heat. But the strange thing is that if I put a load on the GPU (I used Cinebench) after the benchmark is done, the fan returns to ~1000 RPMs and stays there. If I reboot, the fan once again idles at a constant ~2000RPM's

It seems peculiar that once I put a load on the GPU, the fans return to normal - but only after getting loaded up. Any ideas why this is happening?

 

[cdf]

It seems peculiar that once I put a load on the GPU, the fans return to normal - but only after getting loaded up. Any ideas why this is happening?

This is a well known issue, and while it is probably related to the SMC, the exact cause remains unknown. Ideally, we would like Apple to fix the issue, but in the mean time, have a look at AirOut.