Strange noises coming from an air conditioner might be a sign of various problems. A buzzing sound may indicate electrical issues, but rattling or pounding frequently denotes damaged or loose internal components. Possible causes of hissing or bubbling noises include refrigerant leaks. In certain older versions, squealing sounds are usually caused by problems with the belt. In order to stop more damage and guarantee safe operation, it is recommended to turn off the air conditioner and seek expert assistance for a diagnostic and repair.