Ahhhh!
Thanks FBW, all become clear now.
It was, indeed, like a barking dog in the hold... I was struggling to describe the noise in my earlier post. Interestingly, I've heard the "barking dog" a few times before on flights ... in the distance, as though it really was in the hold, but this definitely sounded like a bloody great doberman sitting right beside me (no jokes about my lovely wife, please!) ... VERY loud indeed (again, no wife jokes please)!
Thanks again.
Helo