ULSD = quiter engine

The last two tanks of fuel I have put in my old LB7 have been Shell's Premimum ULSD. Right away after driving a few miles from the station at the first fill up I noticed the injector noise seemed to almost dissappear. When running the LSD the engine is louder.
Anybody got any clues ? Does the ULSD burn at a faster rate than higher sulfur diesel? I put the same amount of PS additive in both at each fillup, so I wouldn't think that had anything to do with it. The engine seems to labor a bit on regular LSD and knock a little louder even when crusing, but with the ULSD it seems to run more free, accelerate easier, and you have to listen carefully to tell its a diesel. Why?

I think you can attribute the new found performance to the "premium" part of the fuel, not the ULSD. Premiums have higher cetane ratings, and that alone will boost performance, smooth and quiet an engine. Unless you've been getting fuel in Mexico, it isn't likely you've been running LSD since before last fall. Texas was one of the states on board early with ULSD. There are still about 1/2 the stations around here w/o ULSD stickers on the pumps, but they are all pumping ULSD. There are no refineries in CA delivering LSD for on road use, and I suspect Texas is the same. A sticker is just a sticker, and most retailers don't (and have never) know or care what they are peddling.