Excessive noise in a motor air cooler can be quite bothersome. One way to diagnose the source of the noise is to listen carefully to determine if it is a rattling, humming, or screeching sound. A rattling noise might indicate loose parts within the cooler. For instance, bolts or screws may have become loose over time due to vibrations. Tightening these loose parts can often reduce the noise. If the noise is a humming sound, it could be related to the fan or the motor. The fan blades might be unbalanced, causing vibrations and noise. Inspecting and re - balancing the fan blades can be a solution. A screeching noise may suggest that there is a problem with the bearings. Lubricating or replacing the bearings can help to eliminate this type of noise.