Sound transmission between apartment units is a common consideration when installing or maintaining air conditioning systems in multi-unit buildings, since compressor and fan noise can travel through shared walls, floors, or structural elements more readily than in a detached house. Anti-vibration rubber mounts placed beneath and around an outdoor unit's mounting brackets absorb a significant portion of the vibration that would otherwise transmit directly into the building structure, and their condition should be checked periodically, since rubber mounts can compress, crack, or degrade over years of continuous vibration exposure.