brakes do not make guns noisier, thats a physical impossibility.
I think what you are asserting is that it is impossible for a brake to increase the amount of energy released as sound and this is probably correct. However, brakes can increase the sound pressure levels at the position of the shooter or for someone in a nearby lane at a range for example. Sound is basically a pressure wave and a brake works by directing the wave in a specific direction, so although the amount of energy converted to "sound" may remain the same the pressure wave is, in effect, focused and so a brake can result in a significant increase of sound energy in specific areas. Because of the design a brake usually directs the pressure wave rearwards and so towards the shooter and anyone standing close by him. As I am sure you are aware you can easily see this in action by watching someone fire a braked rifle and watching the dust and debris get blown backwards by the pressure from the brake, or by standing beside them and feeling the concussion, which is basically the pressure wave, when they fire.
The sound pressure wave, and so the sound pressure level experienced by the ear, with an un-braked rifle is basically a big sphere centred on the muzzle and so the energy in this situation is evenly spread (ignoring the ground and the HF shadow cast by the shooter and other such minor stuff) meaning that people standing an equal distance from the rifle in every direction will experience approximately the same sound pressure level, and the same potential for damage to hearing.
I used to have measurements for the SPLs experienced by the shooter of a braked rifle but I can't find them, however my recollection is that the increase in SPL, noise or whatever you might want to call it is considerable and has the potential to significantly increase damage to hearing.
I would imagine, and I'm just thinking aloud here, that at a significant distance from the shooter of a braked rifle the sound pressure level would pretty much return to an average level approximately centred on the rifle and expanding like a big sphere again as the focused sound or pressure wave is not going to travel far in air, this would be basically an impedance matching problem. So, what you say might be true at longer distances such as in the target butts at a range, but certainly not at the position of the shooter or his mates on the firing point.