My e46 M3 is making the tell-tale whining and groaning of a power steering pump that is either out of PS oil, or gasping it's last breath. The oil level is fine, so I immediately jumped to the conclusion that the pump is bad. The thing that gives me pause is that the noise goes away after a few minutes, which seems odd. Do PS noises like this normally go away? The steering feels totally normal, still.
Also, I have read that a collapsed return line (to the pump) from PS rack could cause the same symptoms. Will a collapsed hose be obvious from a visual inspection? How do I differentiate between a collapsed hose and a bad pump?