From what I can hear, "3" seems to be pronounced like an English short "ă", but further back in the throat. It seems to be more of a "modifier" of other letters' pronunciation, rather than an individual sound itself.
Is the correct pronunciation mumte3 or mumti3? Is There a native speaker that could, please, explain when the diacritic for the vowel "i" is pronounced as such and when as e (ε)? Is it a matter of region or of Duolingo TTS mispronouncing it?