What is the rubber hose coming out of the rear axle?

The rubber hose coming out of the rear axle is typically a breather or vent hose. It allows air to escape and enter the axle housing as the differential fluid expands and contracts, preventing pressure buildup and potential leaks. This hose helps maintain the proper function of the differential and protects it from contaminants. If damaged or blocked, it can lead to differential fluid issues and should be inspected regularly.