My DD did the same thing! I asked around a few ppl and mentioned it to my Dr & he said it was just out of frustration. I guess she was trying (in a weird kinda way) to verbalise that she wasn't happy.

It only ever happened when she didn't get her own way, or would be wanting something that I couldn't understand. I used to just move her & say "we don't do that" she seemed to grow out of it & stopped once she could say basic things like 'drink' etc.

HTH

ps my DH was so help just PHSL whenever she did it