indistincte

/ɛ̃.dis.tɛ̃kt/indistinct
1.
adjectivefeminineSing

unclear, not clearly perceived or well-defined (visually or audibly); vague or muffled

J'ai entendu une voix indistincte au fond du couloir.

I heard an indistinct/muffled voice at the end of the hallway.