Cry:
> Missingno.'s cry is the game's equivalent of a "blank" cry: a Nidoran♂'s cry with a pitch of 0 and no echo. However, a few Missingno. have different cries (specifically 43, 45, 4F, 51, 5E, 5F, 7F, and B5), such as a Rhydon's cry.
Source
Pokedex Entry:
Source