Fan Noise

I have an iMac 2019 27" with a customised SSD. Since I got it, this iMac's fan is really loud and sometimes it went to 3600rpm even when starting the system. I sent it to the apple store and the staff can not find the problem, however they changed the logic board and fan for it. About 3 months later, the same problem came back again. I am devastated and it is a nightmare every time I power on this iMac.

Recently, I installed macOS on the external Disk and start the iMac with this disk. This problem never happened again. I searched online and found many users who have this iMac with customised SSD have the same problem. This does not happen on my own iMac. I don't know if apple can recall this model iMac and fix it.