Is it perhaps the sound of Dogmeat's claws clicking on the ground? I've noticed he clicks rather loudly when he walks.
The reason I ask is that I think I've noticed some "wrong companion" sounds. I recently started traveling with Dogmeat again, and I keep hearing someone softly saying "Well..." behind me. It sounds like it could be Preston--not sure if that's part of his idle pvssyr, since I haven't had him as a companion, but it sounds like his voice. It certainly shouldn't be coming from Dogmeat!
No it's not, if you watch the video you can hear the sound is much different to the sound that Dogmeat would make.
Also I have found a solution and put it in a previous post in this thread.
Sounds like this bug
Please post here to confirm that its not only from Curie
http://www.gamesas.com/topic/1544248-bug-report-index-pc/