I think it is obvious why a pressure wave is produced in front of a moving object but why the rear of it should produce a wave?
As the ship travels through the water, water flows into the low pressure region left by the stern. This is the start of the wave making process from the stern. Turbulence and wave motion occurs.
This is actually a consequence of the equation of continuity, the initial momentum of the water flow along the ship and ending up at the stern is produced by the bow wave.