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How do I find out which app is using up my cpu *while idle*? It stops as soon as I open up task manager

Something on my PC is using up around 25% of my CPU after it's been idle for a while. I know this because my computer glows blue when the CPU is hot (DC controlled LED case fan tied to CPU temp), and I noticed my computer was dark when I was using it, but would be glowing blue if I had left it alone for a while.

I confirmed my suspicions in the CPU usage graphs in Open Hardware Monitor. Something is definitely using the CPU when I'm away, and instantly stopping when I come back.

My first thought was a virus, I've had almost this exact issue before and it turned out to be a bitcoin miner. So the first thing I did was do a full scan with Malwarebytes. But this time, no viruses.

The problem is, I can't figure out which program is doing this, because as soon as I move the mouse or try to bring up task manager, it instantly stops. I even tried using Process Explorer, they have a column that will show a long-term graph of CPU usage for each individual process and handle, and I can't find it in there. I can see "System Idle Process" dip in the graph when this is happening, but no bumps in any of the individual app graphs, not even "System". I can sort by "CPU Time", which is cumulative CPU usage, but there's too many things with too much CPU usage to figure out which one of them it is.

How on earth do I figure out what is making my CPU get hot when idle, when it stops as soon as I bring up task manager?
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  1. Best answer
    have you thought to look in event viewer? It may give a hint as to what is running.

    PC uses idle time to do background processes like Run a defrag, index hdd, run random events I can't think of. Anything it doesn't want to run if you actually using PC. It will also download updates for store apps and windows drivers

    try running bitdefender free and get a 2nd opinion on the virus front
  2. It's just Windows. Try turning off indexing, Superfetch, any and all telemetry crap, etc.
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