I have pretty expensive headphones..professional dj headphones that pick up a lot.
This is what I hear on the call before 911 answers.
It is a child in the background...not an elderly person, not a toddler.
It sounds like a female child say, "He thinks they're dead"
At that point the caller (Vicky??) said, "WHAAAT!!!" (in disbelief), and then says "WHHHAT" again as she starts to cry.
911 then answers. SEE transcript above.
I also think it's interesting the way Brown says more than once "we know someone out there knows something."
Not, we HOPE, or we believe, but we KNOW.