Air purifiers can be noisy as the fans are running in them all the time. When you are planning to buy an air purifier, keep in mind that you might have to deal with loud noises almost all the time in your life after that. If you are not the person who likes a lot of noise around it, you can choose not to buy one or keep it on low settings. If you have kept it on high settings, it will produce loud sounds. Every kind of air purifier has different levels of sounds that it produces, and before you buy one, you can check the sound level beforehand, so you do not regret it afterward. You can also keep them in the rooms where you will not be disturbed a lot. As it has always been advised to keep the air purifiers in your room, you can keep them on low settings when you have them there to avoid the loud noise all night long and getting disturbed. In all other rooms, you can keep them on high settings so you can breathe fresh and pure air but when you are going to sleep, you will also not need so much air to breathe, and the need can be fulfilled with simple low settings, and a lot of problems regarding noise can be solved too. If you are not comfortable while sleeping with this in your room, you might not bring it in or switch it off before sleeping, but it is always a good habit to sleep in the good environment while breathing good quality air all night to keep your organs working just fine.