ZDoom

It's fixed now, probably it was a duplicate of the sound limiting not working issue. But i dunno why, AFAIK that sound pump was only one sound.
https://github.com/coelckers/gzdoom/commit/d4d187e27bb1d2a1f72b4cbb03971b6729cff329

After a bit of investigation for some reason you need to load a pwad, i was playing eviternity this time (updated the OP). It was not the pickup sound but the "Ready" one. After the intermission the cock sound is cut in two and the first part is played at full volume. So it was not that easy to pull this off.
Edit: sometimes the sound is not cut in two but it's still played at full volume. Ouch!

Inventory.PickupSound "weapons/sgpump"
...
Ready:
...
TNT1 A 4 A_PlaySound("weapons/sgpump")

weapons/sgpump STGNPUMP

After the level intermission the weapon select ([s]inventory pickup?[/s]) sound is played at full volume, ingame sound volume settings are ignored even the master slider. I mean that sound is played at current system volume (and also it's cut off). Doesn't happen in vanilla but with a fixed BD v20's shotgun and many other mods i guess. AFAIR it's an ancient ZDoom bug but i hadn't almost noticed it until now. After the accident besides tinnitus a suffer hypersensibility and sound volume control doesn't work on my new laptop (it's a cheap mono speaker) so i can't play unless i mute the sound after every level. To reproduce it changemap doesn't work you need to use the real level exit with the shotgun selected. :?
https://www.moddb.com/mods/brutal-doom/downloads/brutal-doom-v20-legacy-edition (you only need brutalv20b.pk3)
Edit: for some reason you need to load a pwad, this time i was playing eviternity.
https://www.doomworld.com/idgames/levels/doom2/Ports/megawads/eviternity

[code]
Inventory.PickupSound "weapons/sgpump"
...
Ready:
...
TNT1 A 4 A_PlaySound("weapons/sgpump")
[/code]
[code]
weapons/sgpump STGNPUMP
[/code]