Not correct; With an unsuppressed firearm the majority of the noise will be the muzzle blast. Factually, if you are the shooter or within close proximity [probably 100+/- yards] you will most likely not hear any of the sonic crack [bullet breaking the sound barrier] at all as it is completely overshadowed by the intensity and duration of the muzzle blast. You'll need you are a considerable distance down range [usually within a 120 degree cone +/- from the shooter] before the ballistic crack becomes distinguishable. If you've ever pulled targets in a 200, 300, 600 or farther target pit you hear the ballistic crack quite well.
The military actually uses a technique called "crack and thump" to determine distance and range to a single shooter [many times erroneously referred to as a "sniper"]. If the "sniper" has a good suppressor you will hear a "crack" and perhaps a "splat" of the bullet hitting. However, you won't hear the "thump" to get a direction as it is almost impossible to get a direction the shot came from by the crack alone. When you dive for cover the question remains; "am I behind cover or in front of cover?" A very frightful prospect indeed. Now what does this have to do with this discussion? Well, when hunting the game [other than the original target or if you missed] will be just as confused. I've had coyotes just stand and look at their partner who has just been shot or, if the run it is very slow with them stopping shortly to look around. Sometimes they even run over to their buddy to see what's wrong or even run towards me. I've had ground squirrels run over to there buddy with a "what you doin" look just before a bullet finds them.....Animals do the darndest things.....when there is no muzzle blast to spook them. With sub-sonic there isn't even the "crack"......
Now, with all that said, subsonic bullets do make noise flying through the air....a "swoosh" if you will. How loud is dependent on the shape and caliber of the bullet with a given 1050 fps muzzle velocity a 45 caliber RN bullet makes a lot more noise than a 22LR RN bullet flying through the air. A WC or SWC will make more noise than RN. Many times the loudest noise is going to be the action of the firearm functioning, if a semi-automatic, or the bullet striking the target.
As I've mention before, as have others, my sub-sonic suppressed loads are quieter than my springer pellet rifles.