Strange noises can signal a variety of underlying issues:
Bearing failure in the condenser fan or circulation fans. Replace the defective fan motors.
Problems with the compressor pump, e.g. worn bearings. Contact a specialist for diagnosis.
Noise in refrigerant flow due to restriction. This may indicate a low refrigerant level.
The fan blades are hitting the freezer wall due to damage or imbalance. Adjust the fan blades.
Rattling of loose fasteners or panels. Tighten all internal fasteners.