I got in from work and was having an internal rant to myself about all the ways I don't like my job. I could hear mumbling voices and vaguely thought that someone must be watching TV. Then I remembered that I was the only one in the house. I tried to strain my hearing to see if the sounds were coming from somewhere else (from next door, or a car radio being played loudly, maybe) but as soon as I focused on the source of the voices they ceased.
Then I realized that the mumbling sounding a lot like one of my colleagues.

I used to hearing echoes of colleague's conversations just as I'm about to fall asleep at night (hypnogogic hallucinations are very common), and this was very similar. Except I was fully awake and it was 2pm.

I suppose that my conscious mind could have been so focused on ranting that my subconscious went into overdrive.

Any ideas?