My DD started this at about 11mths old too. At this time i ignored it and she soon stopped. She did start it up again 6-8mths down the track and then I would tell her no, which made her stop.

I think it has to do with exploring. They have teeth and they can make a great (not!) noise. It's all a part of growing up.

So I would try telling them no when they do it, or if your happy to ingore it then do that. It will pass soon