not sure if it applies to Metal Slug 5 because I'm not hearing it, but some of the later NeoGeo games were clearly developed using an inaccurate emulator (probably NeoRageX) as part of the development.
As a result Nightmare in the Dark has a really annoying crackle when you jump, it didn't happen in very old versions of MAME, and it didn't happen in NeoRageX, but it did happen once we started emulating actual limits of the chip properly, and it does happen on real hardware (so we emulate it) Not respecting the chip limits actually breaks some other games in worse ways!