Abstract: There is disclosed a system for detecting defects in wheels, tires, bearing and supporting mechanisms of a vehicle. A plurality of microphones is installed in different locations of the vehicle to receive noises or sounds when the vehicle is in motion. The electrical signals converted from the noises or sounds by each microphone are fed to an amplifier and filter circuit. The amplified signals are fed to a loudspeaker located preferably in the compartment of the driver. By sequentially monitoring the levels of the amplified and filtered signals from each microphone or in a pair of microphones, defects in the wheels, tires and bearings can be detected before the occurrence of further damages or accidents. The levels of the amplified signals from each microphone may be displayed simultaneously by an array of light emitting devices.