Because mini-split ACs have separate outdoor units, they are generally much quieter than wall-through or window-mounted AC units. Depending on the model, the noise level of the indoor unit is somewhere between 20dB and 50dB. Generally, you will only hear the smooth whirring noise of the indoor unit. If you are very sensitive to noise, it is preferable to choose a centralized air conditioning system that blows cool air into your bedroom through ducts.