Sorry to burst your bubble guys, but I have personally witnessed a demonstration of sub sonic versus supersonic ammo in a suppressed weapon.
Any object the bullet passes by, even trees, grass, and dirt, will reflect the noise greater than it comes from the gun. In fact, if you stand to the left of and slightly behind a shooter with a suppressor and supersonic ammo, the ear opposite the gun will register the louder noise. Yes, subsonic ammo is distinctly quieter, but there is a wierd advantage to supersonic ammo: the noise of the bullet flying (and impacting!) will mask the sound of the gun's action, hiding the location of the shooter.
Plus, think about it: if someone was hidden well and fired upon you and two other guys without a suppressor, do you really think that you could return fire in the proper direction before you were shot too? (Much less actually hit the guy.) So a suppressor doesn't change the fact you were caught off guard and ambushed.