Due to a series of unfortunate events (fuel line leaks to start with) I had to have all fuel lines and fittings re-sealed/tightened. The MB dealer claimed they were getting a lot of diesels in for similar work ever since the low sulfur diesel fuel came out. Maybe it's not as thick as the old stuff or something. This work quieted the whine down quite a bit. On top of that, the engine had been groaning terribly and vibrating badly while idling. So I had the engine/transmission mounts replaced. This eliminated all the groaning and vibrating, and helped reduce the whine even more, to point where now, 50% of the time I don't even hear it, and the car has once more become a pleasure to drive. Of course, it's cold outside now and I don't know what's going to happen when it heats up in the spring/summer. City start/stop driving during hot summer months seemed to increase the engine groan and whine. So we'll see.........