Thanks for the reactions, Tuesday and srnity!

Tuesday: The reason seems to be the departure of the owners: when they go to work, the dog barks, for instance from 7.30 - 12:00.

srnity: We actually did put a note in their mailbox, which led to a discussion with them at the housing association. The neighbours totally refused to do anything about it...

Ear-plugs don't help enough, we probably have to move... yesterday I had to work till 0:00, was home at 1:00, asleep at 1:30 and waking up again at 7.15 because of that dog!