yeah more teeth on each gear to make them quieter
same deal with R31 skyline 3.7 diff gears
they made 3.73 and 3.7 gears, one was an upgrade to the other as i think the 3.73 gears got noisy pretty quick

my first 1000 had done enough k's to have a recond motor and the diff was noisy,
a couple of others my dad had I drove a bit and dont really remember being too noisy.
My coupe when it had the A10 motor had only a resinator not proper muffler so was too noisy overall to notice the diff. After I put the mild A14 in I abused ita few times standstill 1st and 2nd, spinning into 3rd and when I got the new exhaust and on the road properly the diff has been noisy, mainly when it warms up on the highway.
I treated it with Nulon but didnt help.
I have an H165 waiting to go in sometime eventually.

I ran a H145 alloy carrier diff in the 1000 sedan for 5 years it started life behind a tired A10 then a second hand A12 and finally finished behind an A14 it outlived 2 gearboxes and finally gave up after years of testosterone induced abuse and the addition of 185/15's too much for a little diff.
Previous to it giving up the ghost it provided whine free motoring with out any probs

As others have mentioned as long as you don't abuse them they're light, strong enough and shouldn't make any noise, of course if you hammering round, flat changing and dumping the clutch then they won't last and the steel carrier 1200 one is the go!