Intermittent fans surging on 2020 27" iMac, not under load

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Level 1

60 points

Intermittent fans surging on 2020 27" iMac, not under load

OK, this is a strange one ... and even the Apple tech I talked with on the phone agreed.

I bought a 2020 27" iMac late last year. It's been just fine until a few days ago when the fans started firing up intermittently, when the system wasn't under load. I'm using iStats Menus, and can see the temps and CPU loads in real time, while watching the fan rev up, often past 3600 rpm. (Under normal circumstances, the fans are around 1200 rpm, according to iStat Menus.)

Often the fans roar to life when I start up, and stay there for 10-30 minutes, then they slow down but pulse ... going from the 600s to 2600 rpm for a while before finally calming down. I can put the iMac to sleep, and occasionally while it's asleep the fans kick off ... did it several times last night.

This doesn't just happen at startup; it can occur in the middle of the day. I have standard productivity apps running ... Slack, Outlook, iMessage, Tweetbot. No video rendering or playing. Killing all apps doesn't necessarily stop the fans.

I have closed all apps, and closed all Menu Bar and background apps - still happens. I have reset the SMC on the iMac. Still does it.

I have another user profile on this computer, and when I switch to that, it doesn't happen; at least, not for the brief time I'm in it. If the fans are revving when I make the switch, they roar for a while and then calm down soon after the switch.

The tech I talked to had me go into safe boot to see if that would clear it up, but of course at the time I was talking to him it wasn't doing this. He went off to talk to colleagues several times, and came away stumped.

This is a stock iMac, 16 GB of RAM, 1 TB SSD, 3.3 GHz 6-Core Intel Core i5. I have a HooToo hub and Seagate SSD attached to it, but they've been there for months (the hub since I got the iMac) and have not caused issues.

The problem began while I was on macOS 11.4, and upgrading to 11.5 did not fix it.

I've attached a screen shot from iStat Menus showing what this looks like in a graph.

Posted on Jul 23, 2021 6:26 AM

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Answer 1

Jack-19

Level 8

45,694 points

Jul 23, 2021 6:29 AM in response to LeVeau

Welcome to Apple Support Communities.

Please Use Apple Diagnostics to test your Mac - Apple Support, and report back what the Reference Code is.

Also, I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to diagnose and identify issues, both hardware and software. It is trusted by many users. Please follow the steps outlined below:

Navigate to: https://etrecheck.com and get the free version of EtreCheckPro.
Download it. It is a free and trusted app. It is often recommended here on Apple Support Communities.
Open EtreCheck, and before running the report, be sure to check “Allow full Drive Access” at the bottom of the EtreCheckPro window.
Run the report, and put it in a post, as seen here: https://discussions.apple.com/docs/DOC-250000211. We will then examine the report for issues in your Mac.

Jack

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Answer 2

Jack-19

Level 8

45,694 points

Jul 23, 2021 8:09 AM in response to LeVeau

EtreCheck notes:

Unsigned files - Possible adware Run a scan with Malwarebytes.
Configuration profiles found This may be malware. Go to System Preferences > "Profiles" and remove them if unknown.
Runaway user process This may go away with a restart.
Delete Western Digital software.

By the way, the fans were pulsing while the Apple Diagnostics were running.

That is normal, as it is testing the fans.

At this point, since the Mac is newer, I would recommend you make a Genius Bar appointment at an Apple Store and have them look at it: Apple Store - Find a Store - Apple and Get Support.

Jack

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Answer 3

LeVeau Author

Level 1

60 points

Jul 23, 2021 7:59 AM in response to LeVeau

EtreCheck report on fans issue.

Thanks for the EtreCheck and Apple Diagnostics suggestions. Did both, the EtreCheck report is attached to this post. I removed some files as recommended in the initial version of the report. This is posted after having done that.

No issues found in the diagnostics run, ADP0000.

By the way, the fans were pulsing while the Apple Diagnostics were running.

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Answer 4

Allan Jones

Level 9

68,780 points

Jul 23, 2021 8:29 AM in response to LeVeau

This is a clue:

Top Processes Snapshot by CPU:

Process (count) CPU (Source - Location)

mdworker_shared (57) 393.82 % (Apple)

mds 94.52 % (Apple)

mdsync 16.00 % (Apple)

kernel_task 12.52 % (Apple)

mds_stores 12.26 % (Apple)

"md" processes are part of Spotlight, usually driving its indexing function. They are very active immediately after a restart. If you run another EtreCheck test after a restart, do it after the computer has been idle for 20-30 minutes. Under normal conditions, even following the updating of big packages like MS Office, that should be more than enough time to complete the indexing tasks.

You can use Activity Monitor (in Applications > Utilities) to see if the md tasks have settled down. See:

Activity Monitor User Guide for Mac - Apple Support

The intermittent nature of the fan cycling could be two two things:

1) the detected internal temps are right at the point that turns on the fans; the fans come on a short time to drop the temps below the trigger point. Then some process keeps the temps up, again triggering the fan again.

2) more likely, some "phone home" app is periodically doing its thing and that is increasing the fan speed for short period.s during the day. Were I to hazard a wild guess, I'd say MS OneDrive and/or Google Backup and Sync.

However, the many system modifications you have could also be tripping up the heat regulation system.

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Answer 5

LeVeau Author

Level 1

60 points

Aug 6, 2021 6:51 AM in response to LeVeau

Another update.

The new Belkin hub did NOT fix the problem, nor did running it without a hub at all. But ... the problem appears to have just vanished.

Last Sunday, both the roaring and pulsing behaviors stopped. The fan has behaved ever since, as you can see in the attached chart. I'm happy, but also wary, because something caused this to happen, and I do believe there's a hardware issue lurking somewhere.

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Answer 6

LeVeau Author

Level 1

60 points

Jul 23, 2021 8:17 AM in response to Jack-19

Unsigned files - Possible adware • Run a scan with Malwarebytes.

Have done that. No adware. The unsigned files indicated are Parallels VMs.

Configuration profiles found • This may be malware. Go to System Preferences > "Profiles" and remove them if unknown.

Nope. They are configuration files related to the Prey Project, an anti-theft app.

Runaway user process • This may go away with a restart.

Have restarted a bunch. Nope.

Delete Western Digital software.

None on my system.

By the way, the fans were pulsing while the Apple Diagnostics were running.

That is normal, as it is testing the fans.

They were pulsing before the diagnostics started running, same behavior as when I'm in my profile - which says to me it's not software-related.

At this point, since the Mac is newer, I would recommend you make a Genius Bar appointment at an Apple Store

Ugh, yeah, I am about to come to that conclusion. Schlepping a 27" iMac around is no fun.

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Answer 7

LeVeau Author

Level 1

60 points

Jul 23, 2021 10:57 AM in response to LeVeau

I ran the Apple Diagnostic again. The fans are not slowing down or "pulsing", and they were going full bore when I did the diagnostic. Got two error codes, and a note that "There may be a problem with the fan." Gee, Apple, ya think?

Codes: PPF004 and PPF003

It's now doing it in safe boot, in the other profile I have on the iMac, and during the diagnostic. So yeah, looks like an Apple Store visit for me. 😢

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Answer 8

LeVeau Author

Level 1

60 points

Jul 27, 2021 8:36 AM in response to LeVeau

Here's an update on this issue:

I took the iMac to the Apple Store. They kept it for a few days and, of course, could not replicate the problem. They also felt compelled to format my HD and reinstall the OS. I let them, though I knew it wasn't going to do any good. I picked it up yesterday, ran a Time Machine restore (p.s., I love Time Machine!).

After a couple of hours, heard the fans again, while the system was sleeping. They also roared for a short time this a.m.

I've been talking about this issue on Twitter, and one of my followers this morning mentioned that he'd had the same problem on a MacBook Pro, and traced it to his USB-C hub that was powering Ethernet and a second monitor via HDMI. He got rid of the hub and it fixed the problem. Well, I have a USB-C hub for a second monitor, an off-brand called HooToo that has gotten good reviews. I swapped it out this morning for a Belkin hub and, so far, no fan activity.

Too early to say I've solved the problem, but I did not take the hub to the Apple Store with the iMac. I'll give it a couple of days, but I am hopeful.

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Answer 9

LeVeau Author

Level 1

60 points

Aug 7, 2021 9:16 AM in response to LeVeau

I asked on Facebook about possible causes of this (I've got a fairly tech-savvy group of friends/followers), and someone suggested animal hair. I've got two cats and their hair covers everything.

That person suggested that the fan's pulsing may be part of a routine that detects an obstruction or gunk in the fan mechanism and speeds up, slows down to dislodge it. He said he had similar pulsing in a MacBook Pro, opened it up and found it was gunked up with cat hair.

I'm going to try to vacuum it out through the vents in the back. It's still behaving at the moment, but I figure the vacuum can't hurt. Can it?

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Answer 10

LeVeau Author

Level 1

60 points

Sep 12, 2021 7:58 AM in response to LeVeau

An update to this issue:

Took the iMac into the store for the second time, and the Genius checking me in ordered a new fan. It was installed and I got the iMac back yesterday. So far, it appears to be fixed.

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Answer 11

Jack-19

Level 8

45,694 points

Jul 23, 2021 8:21 AM in response to LeVeau

None on my system.

Yes, here: Executable: /Library/PrivilegedHelperTools/com.wdc.WDPrivilegedHelper

But yes, I think going to the Genius Bar is the right next move.

Jack

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Intermittent fans surging on 2020 27" iMac, not under load

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