The curious incident of the dog that won't stop barking

The dog upstairs is driving me spare. He barks for what feels like several hours a day. He barks when he's left alone, and he barks when his owners are home. he barks when he's being taken for a walk, and he barks when he's coming home from his walk. He barks ALL THE TIME.

I have considered saying something to his owners, but, you know, what can they do? I don't think they leave him alone for hours on end or anything. There's also the fact that only one member of the family seems in any way confident with English and she also happens to be deaf, so communication is really very challenging. But even if there were no communication problems, I don't know what they could do about their pet's habits. He's a dog, he barks. He is a West Highland terrier and like many small dogs, he makes up for his lack of size with a particularly piercing and loud bark. The hallway is concrete and provides the perfect amplification. The worst thing is, now that I've noticed it, I can't un-notice it, so it drives me even more crazy.

Any suggestions? And happy Friday ...