Sometimes my computer makes noises like a small motor is running, it comes and goes. Why does it do that?
I'm no help,but my dinosaur of a computer will grind away and there for a while a fan was making some noise. The fan noise comes and go. This thing just keeps on going. I would not know what to do if I had a computer that was quiet. I really only use it to get on the FF.
Sounds to me like the cooling fan. If you didn't notice it before, you just might not have noticed it. Is it a desktop or a laptop? Laptops should be named something else. Using them on a laptop or on any soft service it not good as they can't dissipate heat. They should be used on a hard service, preferably on a rack that lets air under them. On a desk top, dust is the enemy. Especially if your cpu sits on the floor. It should have regular maintenance to keep it clean. Shut it off, unplug it, take the side cover out and use a can of air to thoroughly blow it out. Be sure to clean the venting slots on the case as well. Dust will create heat not to mention other serious problems. Usually if you start hearing the cooling fan all the time, it is a dirty computer.
It's a desk top, with everything built in behind the screen.
Still could be dust. Look behind (under?) it at the cooling slots. If they are full of dust, you may have found your issue.
Dust, or the bearings in one of the little fans are worn out. Dust messes with the cooling, things get warmer and the fan speeds up to compensate. If the bearings are shot, all sorts of weird noises.
Desktop, laptop, all in one. All have heatsinks and fans. Desktops generally have a bigger heatsink and fan, so you have less problems.
But the first step is to get the back cover food, brush / blow any dust away, and see how the fans are running. If there are several, put your finger on the hub of each one and see if the noise stops. They are usually standard sizes and you can buy generic replacements for most of them.
While I agree with dust or a fan being the most likely cause, a failing hard drive can also become noisy. Make sure your data is backed up.