I can assure you that three instances of muttering is nothing out of the ordinary! Couldn't tell you how many people mumble to themselves where I work. Usually, if someone is muttering quietly it means that they're pretty much in their own heads, half-way oblivious to their surroundings.
I'd go as far as to call it a great sign!! Unless you specifically hear them mumbling something about odor/smell/shit whatever, but you mentioned you're very in tune to that and would notice, so in this case I think it's indeed a great sign.
Glad to hear things are looking up for you Hope, keep us posted on your improvements!