Strange sounds

    This isn't a big deal; but it did happen and it was a definite sound.  Today, in the early afternoon; I decided to go to the master bedroom and read a new book that I had purchased yesterday. The dogs were left downstairs, both taking their afternoon naps, but I implaced the gate on the stairs, as I went up, anyway. My wife was watching TV in the Den. I hadn't much more than settled in and read about one page when I heard what sounded exactly like my dog shaking himself and rattling the tags on his collar. So I said," Get up here" and thumped the bed as I do when I invite the dogs upon the bed. There was no response (normally I'd get a very rambunkious reponse). I immediately got up and looked for my older male (thats who it sounded like). There was no dog to be seen. So this is the first strange effect for some time. As it may not seem significant, it is  a mystery. Later when I returned downstairs, I saw the gate was still securely in place. Both dogs greeted me in typical bouncey fashion when I returned from upstairs. I have no idea what the sound was. I cannot think of anything that would make such a characteristic sound, other than a dog shaking itself.