You also need to remember that it is only in the last 10 years or so that diesel technology has advanced since probably 1930. Listen to a new highway tractor, and watch the stacks compared to ten years ago. No smoke, quiet, powerful, economical- all due to the electronic controls added. The new GM pickup diesel uses "common rail" injectors, which I presume means electronic, and it would not surprise me if they use a knock sensor tuned to specific resonances- even a gas engine must use a specific knock sensor based on engine type, sensor location,etc.