Maybe grumpy chatty bats? Researchers “Translate” Bat Talk. Turns Out, They Argue—A Lot https://www.smithsonianmag.com/smar...nslate-bat-talk-and-they-argue-lot-180961564/ You buying it?
Yes… they are mammals and sonar plays no role in tight sleeping groups. So it is probable that these bats talk. At least to those bats who listen.
According to the research alluded to, baby bats babble - much as human babies do. That makes me happy - I always thought the babies were cute. As the former official bat catcher on a couple of worksites that possibility is something I wish I had known.