A Mac that sounds like it is about to take off is doing exactly what it was built to do. The fans are the response, not the problem, and the useful question is what they are responding to. Two minutes in a window that is already on your Mac usually answers it.
First: the fans are not the fault
Apple describes the behaviour plainly in its page on fan noise on a Mac: the fans run faster to keep internal temperatures at a normal operating level. A machine that never spun them up under load would be the one worth worrying about.
So the goal is not to silence the fans. It is to find what is producing the heat, and then decide whether that thing is worth it.
Second: ask the Mac which process it is
Open Activity Monitor, which lives in Applications, then Utilities. Apple documents it in the Activity Monitor user guide. Click the CPU tab, then click the CPU percentage column header so the heaviest process sits at the top.
Leave it there for thirty seconds rather than reading the first number you see. Processes spike. What you want is the one that stays at the top while you watch, because that is the one the fans are answering.
Third: the column that matters, and the one that misleads
CPU percentage is the one tied to heat. Memory is not, and this is where most people go wrong: a Mac using almost all its memory is a Mac using the memory it has, which is normal and produces no heat on its own.
Two names come up constantly and mean something specific. A process called mdworker or mds is Spotlight building its search index, which happens after a big update or a large file copy and finishes on its own. A browser near the top is usually one tab, not the browser, and most browsers have their own task manager that will tell you which one.
Fourth: when it is not software at all
Three causes produce the same noise and will not appear in any window. A blocked vent is the first, and on most laptops the vents are at the back and underneath, which a bed or a sofa covers completely. Ambient heat is the second: Apple specifies an operating range, and a hot room pushes the fans up with no process to blame.
The third is dust, which accumulates over years and is the reason a machine that was quiet for three years is not quiet now. That one is a service visit and not a setting.
There is one case Apple treats separately: fans running fast while the machine is idle and well ventilated. For an Apple silicon Mac the suggestion is to close and open the laptop lid, or restart. For an Intel Mac it is to reset the System Management Controller, which is the chip that governs the fans among other things.
If the window does not look like this
Older versions of macOS put an Energy tab next to CPU, which is worth a look on a laptop because it separates what is draining the battery from what is heating the machine. Newer versions fold that into the CPU and Energy tabs. The Applications, then Utilities path has not changed in many years.
What this does not fix
Apps that promise to control the fans directly are the thing to avoid here. They override a safety system to hide a symptom, and the symptom is the only warning you get before thermal throttling, which is the machine slowing itself down to stay cool. If the fans are loud because something is working hard, that is the system behaving correctly.
If the noise started around the same time the machine filled up, those two are related more often than people expect, because a nearly full disk makes the system work harder for ordinary things. What System Data actually holds covers the storage side of that, including the part you can genuinely recover.
Last updated October 14, 2026