is it common for my 2 year old to mumble? he has a pretty good vocabulary, repeats new words, combines words, etc. Lately he has been very soft spoken and mumbling a lot especially in group setting and with new people, i can't tell what he's saying half the time because he's mumbling and talking quietly. He will not mumble when he's super excited about something. It's been going on for only 2 months or so he never did this before.