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macrumors newbie
Original poster
Oct 19, 2019
My hard disk is continuously reading/writing and making a "tickling" sound. Activity Monitor shows little CPU or disk activity. The most active process when "inactive" is generally WindowServer (or kernel_task). This has been happening since before I upgraded to Catalina, but is worse now.

What's going on?

1. Has something taken over my Mac? (The activity continues if I disconnect from Internet for 1/2 hour. I've run an anti-virus scan; result: nothing.)

2. Is it continuously filling some cache or other?

3. Is it indexing for Spotlight? (No, I have put "Macintosh HD" in System Preferences > Spotlight > Privacy > [block list]).

4. Do most modern Macs come with SSD rather than rotary drives, and Catalina assumes that?


P.S. This is a late-2012 iMac with 8Gb RAM, 27" screen, 1TB hard disk.


macrumors Penryn
Feb 20, 2009
The answer is mostly 2 and 4.

The hard reality:
Modern versions of the Mac OS (actually, starting back with Mavericks) do not mix well with platter-based hard drives.

The OS is "hitting the drive" much more frequently, perhaps almost continuously in some situations.
Thus, the "disk thrashing" with platter based HDD's and the OS.

The best way to get rid of this:
Replace the HDD with an SSD.
That will fix things IMMEDIATELY.

I believe your late-2012 iMac has USB3.
The fastest, easiest, cheapest way to get it running smoothly again is to buy an EXTERNAL USB3 SSD, plug it in, and set it up to be the boot drive.

The prices on 1tb USB3 SSDs have come down considerably.
That's what I'd suggest that you get.
You can get a Samsung t5 or Sandisk Extreme (ready-to-go)
You could get a "bare" 2.5" SSD, an external USB3 enclosure, and assemble the drive yourself.

Once you have the drive, do this:
1. Connect to the iMac
2. Open Disk Utility and erase it to APFS.
3. Next, download CarbonCopyCloner from here:
(CCC is FREE to download and use for 30 days, this costs you nothing)
4. Use CCC to clone the contents of the internal drive to the SSD (will take a little while if you have a lot to clone over)
5. Go to the startup disk preference pane and set the SSD to be the new boot drive
6. Reboot.

Also worth mentioning:
You could open up the iMac and install the SSD internally, but there's risk of breaking something if you run into trouble.
You'll get about 85% of the speed (from the SSD) going the "USB3" way (outside) vis-a-vis installing it internally.
That's close enough to be "the better way" for me.


macrumors 68040
Sep 2, 2013
North Vancouver
A clicking hard drive can be a sign that the drive is starting to fail or has problems. See this link

Might be a good time to make sure you have a current back up as mentioned above (and update to SSD ?)

I have had 2 HDD drives fail in tha past 10 years - both started clicking before they failed - hopefully that is not the case with your iMac.
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