Diesels tend to run at significantly lower RPM, and with lower valve spring pressures. The gears are also engineered to be durable, instead of being designed specifically to make noise and impress children.
Some aftermarket gear drives can be acceptable in some forms of racing; but those gear drives again have some "real" engineering, rather than the "slap this on, it sounds just like a blower" "engineering".
It's exactly like axle ring-and-pinion gears. If the gearset is noisy, the gears are not meshing properly. And this is INTENTIONAL on bottom-feeder gear drives.