Until today, I have almost never heard the fans on my iMac Pro (10-core), other than a faint background whirring. Now I am hearing them very distinctly when running Handbrake. I've run Handbrake many times in near silence. The fans are running between 1450 and 1650 rpm, temperature between 93 and 95 C., and processor between 3.6 and 3.8 GHz. I can hear the fans at 1450, but not loud, quite apparent at 1550, and too loud at 1650. The only change to the computer between yesterday and today is that I installed 10.13.4 this morning. Could that be the reason?
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iMac Pro iMac Pro Fan Noise
- Thread starter FredT2
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Interesting. I have done lots of transcoding with my 10-core Vega 64 iMP, but only with FCPX 10.4 and only on 10.13.3. I rarely hear the fan but once or twice it spun up briefly.
Unfortunately I can't test 10.13.4 right now since my iMP developed an apparent GPU problem causing thermal dependent graphical corruption, so it's having the logic board replaced.
10.13.4 may have included Intel microcode updates, probably refinements to the Meltdown/Spectre fixes.
The fix list for 10.13.4 included a "graphical corruption problem" on the iMac Pro. I hope the fix wasn't to run the fan more.
The problem with microcode updates is I don't know if you can revert that. You could make an image backup of your boot drive, revert back to 10.13.3, but that doesn't totally restore the state if microcode updates are installed.
Have ambient temps been about the same in each scenario? Your temps under load are near the thermal limit of the CPUs, so it stands to reason that the fans would start kicking in.
Yes, same temps before and after.
Update: I tried running previous version off of a backup, but either something is wrong with the backup or previous version is no longer compatible, because it didn't work. Took forever to boot then nothing but continual spinning balls.
Unrelated to fans but is maybe to 10.13.4: is screen brightness on boot now brighter? I keep my brightness fairly low so never previously noticed that one corner of the display has major light bleed when the Mac logo comes on. I thought my display was perfect.
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You’d have to restore from a Time Machine backup, or boot from or restore from or image backup. I have restored my iMac system drive from a TM backup but not after a microcode update.
If you have an image backup you can usually just boot from that, which avoids the risk of reloading the system drive.
Restoring includes reformatting the boot drive. So at that point you are totally dependent on the backup. If the backup drive has an error, you are hosed. That is why I always have two different backups.
I don't know of any way to revert versions of macOS except restoring from an older backup or booting from an older image backup. If you have a Carbon Copy backup of your 10.13.3 boot drive you can just boot from that. Yes you'd need a good backup for that. My iMac Pro will be back from repairs in a few days and I'll try it then.
How to boot from a different startup disk: https://support.apple.com/en-us/HT202796
