Change sounds

[TFEF]

C:/Program Files/Amnesia - The Dark Descent/redist/sounds/ui/ui_terror_meter.ogg

I think it's this sound you're talking about. This is the somewhat screechy sort of sound that plays when monsters see you. If you're on Steam, it should be something like C:/Program Files/Steam/steamapps/Amnesia/redist/sounds/ui/ui_terror_meter.ogg.

Although, I really would recommend playing through the game properly first without modifying the files.