For noise on a 24V, it all has to do with the injection pump, injector style, and injection pulses.
A 12V with a P7100 or a 24V with a VP44 relies on the injection pump to individually pressurized each line, and mechanically pop open the injector. That right there introduces a lot of noise from the mechanical operation of the injectors, with metal shuttle valve and spring clanking around via hydraulic pressure. Due to this mechanical-hydraulic operation, there can only be one injection pulse per piston cycle, so it ends up being a big hit all at once in the combustion chamber.. another source for noise. This can be tamed a bit by retarding the injection event to be less-advanced relative to piston TDC.. but that goes against what a lot of the hotboiiiiss want with their coal-rolling diesel street race trucks that need to make maximum power at all times. Generally speaking, the less advance on the injection timing the easier cold starts are, the quieter the injection "hit" event is, but also some top end power is lost (not enough to be a concern for a 'street' truck, IMHO).
A 5.9L commonrail, or the 6.7L, or anything after.. all have a constant-duty high pressure pump (CP3) that is tiny and is constantly pressurizing a common fuel rail to a certain pressure, and the injectors are electronically-controlled, and the operation of the injectors' solenoids is very quiet. This means per piston cycle, you can (and they do come like this from the factory) have multiple fuel injections per piston event. A little injection early on, to start some combustion and start raising cylinder pressure.. so that a later injection (or two) can happen with a smaller amount of fuel overall yet still hitting the cylinder pressures needed to extract the power from the diesel, with less-harsh combustions per injection. This leads to cleaner emissions, more efficient burn, significantly less noise, but also some hotter engine temps generally speaking (have you ever seen the size of a 3rd gen radiator?.. it's like 4ft tall).
For mechanical noise, the 24V is known to have a very thin single-wall oil pan, that lets a LOT of this knocking noise out through it. I haven't confirmed it personally, but I've read multiple times that the older 1st gen 12V engines had a dual-wall steel pan as an attempt to reduce the noise, as well as the 3rd gen and newer oil pans being dual-wall.
On 4th gen and newer Dodges they really started paying attention to NVH since these trucks became pretty popular as more than just a heavy duty work truck, so there is sound and heat insulation everywhere in the engine bay and the cab, and the factory intake piping has all kinds of engineered passages and ribs to limit combustion noise from radiating out the intake end.. and the factory exhaust on a 4th gen... well.. holy... you better just Google that to see what they look like haha.
But I digress. The Nova is crazy for sure.. everything I know about tuning, fabrication, general wrenching.. I taught myself on that car. I got it as a grad present from my parents at age 17 in 2004, and have been building it ever since. From the factory it was an inline-6 3spd on the column car in 'grandma green' interior/exterior, but when I got it the previous owner had swapped a 305ci/TH350 combo into it, with some Chevelle bucket seats, crappily spray painted it orange (I guess to make it sell easier?) but kept the factory open rear 8.2" 10bolt, factory manual steering, and factory manual drum-drum brakes. And then I started taking it apart and learning on it!
