One problem related to crankcase (pcv) has been reported for the 2005 Volvo S40. The most recently reported issues are listed below.
The contact owns a 2005 Volvo S40. While driving low speeds, the engine makes a howling noise. The noise stops while driving higher speeds. The dealer stated that there was an oil trap (pcv system) in the intake manifold that was clogged and could cause the crank case to fail. The failure mileage was unknown.