I think hearing loss is not going to be a concern if your life is on the line and you need to fire a few rounds in the house.

Now if you are practicing room clearing in a shoot house you should be wearing hearing protection either way.

That said the 9mm carbine with 147 grain sub-sonic loads are actually very quiet compared to a 16" 223....I mean very quiet.

Do you already have a 9mm upper?
They are very accurate...even out to 100 yards, but the recoil will surprise you....it's almost the same as the 223. I recommend the Oly over the Colt/RRA style as it does not need a dedicated lower.

A 9mm in a carbine is very adequate for personal defense under 100 yards. It's not fair to even compare with the pistol 9mm....if you reload you can get energy and velocity exceeding the 357 magnum.