As mentioned briefly in the Discord, I am formally reporting the title problem and its solution.

Description: Scancode.123(no convert in JIS IME), 46, 48(Volume up/down) keys will sound the minigun spin-down. like this: video
Solution: update PneumaticCraft to v6.0.7 (pneumaticcraft-repressurized 6.0.7+mc1.20.1) Changelog
v6.0.6 does NOT fix this issue in my test.