I find my Icelandic chicks are vocal in different ways than the other breeds I've raised. Cockerels mature much more quickly and pullets "talk" as they go about the yard. I think the sound you heard is a cockerel "calling" the others, most likely to alert them that something has changed (you or your wife entering the room).
I know I may be biased, but, I think the Icelandics just aren't like other chickens in many ways. They seem to have a way of communicating that is uncanny. I've read that chickens don't have much of a memory but my flock definitely remembers things....like when I bring a cardboard box into the coop to remove someone (last time was last night and the time before was Sept of last year). Audun started with an alert noise and the hens picked it up. They know someone has been "gotten" in the past when the box appeared and know it is a sign of "danger". I bring things through their end of the barn all the time and they don't worry about it but they know the box means something.....also the large fishing net I use to catch young cockerels always causes the danger signal alert. The chicks out the yard with their moms will freeze solid when the alert call is given and stay that way until "released" by their mom or will scatter if she "tells" them to. They aren't your typical pet chicken......and that is why we love them so much......even when they roost on houses and tractors, or nest in shavings bags, or insist on creeping into the other side of the barn to eat the cats' food, or escape at every opportunity......Life is better with Icelandics!!
