I would start off slowly, like Karen said. Just introduce yourself, learn a little about the family & dog & share some knowledge on your 1/2 as well. to mention it slowly try saying something like Karen said like "oh i noticed your dog seems a little disturbed by your move"

If he continues to bark & bash after a few weeks, then I would again go over there & in a nice way say something like "geese your dog seems to have a hard time adjusting" maybe offer to reccomened a couple of local reputable obedience class instructors or behavorist. Ask if you can help.

believe me I know this first hand, when I forst got my rott she would bark but ONLY when I was not home, not one of my neighbors have ever said anything to me not once, then one day the local dog warden came a knocking at my door saying how he has had neumeous complaints, luckily he was nice & understood & believed me when I told him I had no clue it was going on as my dog only behaved like that when I was not at home. Luckily I was able to nip that problem in the rear & it is behind us now. But w/ the world nowadays no one has neighbors like they used to, I would of loved to have one of my neighbors come over & tell me what was going on.