Once when I flew with my dog (he was flying in the hold as cargo), HE was the barking dog--although I suspect no one else even noticed. He was below decks in his crate, and about halfway through the flight, I heard an odd, faint, repetitive sound coming from under my feet. Leaning down I could hear it better, and upon reflection, recognized my dog's "anguish" bark. It was barely audible from the cabin, but I knew what it was. He went on for a good half-hour. I was pretty anguished myself by the time we landed. I guess the doggie Valium had worn off. Thank goodness, he was none the worse for wear.

I've seen dogs in the cabin plenty of times but never been disturbed by barking. They seem to be a lot quieter than children, and a lot of adults.