Until every one of us can afford to have central a/c installed in our home, we have to get by with several window a/c’s. It’s better than nothing, of course, but they can be entirely noisy! First, there’s the hum of the fan under ordinary operation. Then, when the compressor comes on, there’s a thunking noise. Until I got used to it, every time the compressor in our living room switched on, the thunk would wake me up! And every so often, I have had to adjust the fitting in the window because a rattling noise occurs. Occasionally, I’ll thumb through the owner’s manual and stumble upon an item that I overlooked when installing the a/c’s. For one, I realized you should pay special attention to any gaskets as a bad install can lead to a rattling noise. Also, any vibrating noises might be linked to suspect tightening of the mounting screws. Or rattling may result from the glass panels in the window, which can be eliminated by applying window putty. Occasionally, there are noises that come from inside the unit. The manual suggested that I check the mounting parts for official tightening, or that I slightly reposition the device itself. A friend of mine who works in the Heating and Cooling Industry once mentioned that if the fan blades get dirty, it will cause them to get out of balance. Once this occurs, it wears out the bearings. In the end, I realize that some of the existing window a/c’s are getting older. This alone explains why the units are noisier than the newer models. All of these things remind me to keep saving my pennies so that I can afford central a/c for my home someday!