I have noticed when playing the dev build that the MP5 is actually being treated as an unsuppressed weapon.
Shooting the weapon at long distance from enemies can still alert them and the reverb applied to the gunfire is identical to the one applied to unsuppressed weapons. Sound mods have no effect on this issue.
note: I used enhanced soundscape in the video for the sake of clarity as the reverb is much more audible with that mod. I tested it both with and without sound mods. It happens in both cases. The M1911 in the video is just for comparision purposes.