Sounds to me like you have a computer that’s running fairly hot.
Most computers have a temperature sensor and a variable-speed fan. As your machine runs, it keeps an eye on how warm it is and decides at what speed to run the fan.
It sounds like your machine is getting hot quickly and tries to cool itself off by running the fan at full speed. That cools it down somewhat so the fan can be slowed down, but then it heats up again and it’s full speed (fan) ahead!
The real question here isn’t why your fan runs so much, but why is your computer getting so hot? There are several reasons why this might be happening.
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Reason #1: Blocked air vents
Sometimes, dust, dirt, and other debris block the air vents of your computer and it can’t create enough air flow to cool down efficiently. The fan makes some difference, but the problem simply could be that it can’t dissipate the heat fast enough so the computer just stays too warm.
In a situation like this, I recommend that you take a look at the air vents in and around the computer. Make sure they’re clean and have good airflow.
If you were on a desktop, my suggestion would be to pop it open and see what kind of dust and debris have accumulated within the machine and on the CPU’s heat sink. Because you have a laptop, doing this is a little bit more difficult and not always practical.
Reason #2: Your computer’s just working hard
If you’re doing something that is CPU intensive, such as video work, running a game, or some other heavy-duty task, your machine will get hot. That happens when your processor is doing a lot of calculation.
In this case, it’s normal that the fan will kick in to keep the computer running at a normal speed. That’s why this whole heat-prevention scenario exists. A hard working CPU generates heat, and the fan and cooling system dissipate that heat.
Reason #3: Something else is using the CPU
So, let’s say dust and debris aren’t the problem and you’re not doing anything CPU intensive, but your fan is still running at high speed. In this case, it’s possible that some other program on your computer is accessing the CPU. It could be expected or unexpected. It could be malware.
We don’t know, but we do need to find out. So, I’m going to point you to an article, “How do I find out what program is using all my CPU?”
This will instruct you to download a task manager replacement called Process Explorer that will show you all of the programs running on your computer, and show you how to sort them by CPU usage. If you find that some program is hogging most or all of the CPU, that may be what’s causing your CPU to run hot and the fan to run at full speed.
What happens next, of course, depends on what you find. It might be expected, it might be something in your control that you can disable or remove, or it might be malware in which case you’d take the appropriate steps to remove it as well.