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I have noticed this pattern quite a lot during the last few months or so. When I'm doing low-load tasks like writing emails, reading wikipedia or editing my timetable, the CPU fan will suddenly start to run at high speed. When I open the task manager to see what's going on, I see a 80-90% load for like half a second before it immediately drops to almost zero. It's strange, it feels like I caught my PC doing something it's not supposed to do.

This has happened way too often in very similar situations to be just a coincidence. What could be the reason for this behavior?

This question sounds exactly the same, but it is not a duplicate. My CPU load is high before opening the task manager, and in the other question it spikes after opening the task manager and then quickly returns to normal.

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    my first instinct is that you have a coin-miner running and its trying to escape notice. you may have slightly better luck running tasklist > c:\tasks.txt to record the list of running tasks. How is your antivirus looking?
    – Frank Thomas
    Jan 24, 2021 at 22:26
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    It could also be Windows Search Indexer or Defender AV starting up when the load is low. You might set Process Monitor, docs.microsoft.com/en-us/sysinternals/downloads/procmon , to run in the background, and record what is using CPU.
    – DrMoishe Pippik
    Jan 25, 2021 at 0:53

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Your question does not really match your text because the Text says CPU is high before opening Task Manager.

Open Admin Tools, Resource Monitor. Be sure the CPU line is expanded. Let it run for 10 - 15 minutes and see what process is causing the CPU.

Resource Monitor is an excellent tool for this problem.

This is Windows 10 and so you may wish to run a Full Scan with Windows Defender, and restart the computer before running Resource Monitor.

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    Note however that some malware will remain inactive if certian processes are found to be running, like taskmanager, resource monitor, process explorer/cpumon, etc. this answer is very helpful in tracking down the issue if it is in fact legit software, but may not show anything that wants to hide, so just keep that in mind if the activity you are looking for never manifests in Resource Monitor.
    – Frank Thomas
    Jan 24, 2021 at 23:20
  • In response to your advice, I did add a short paragraph to run a full scan with Windows Defender first.
    – John
    Jan 24, 2021 at 23:24
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    I don't get in what way my question doesn't match my text, but I will try the tool.
    – MaxD
    Jan 25, 2021 at 8:53
  • Opening Task Manager and high CPU drops to normal (Title) is normal with Windows 10. But your question text says CPU was already high and then drops with Task Manager. That is not entirely normal. Try looking at resource monitor and see if you can pin down the process.
    – John
    Jan 25, 2021 at 11:30

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