Sorry to hear you're having issues with the new shotgun. Any mass manufactured product can have problems from time to time that factory QC doesn't catch. What matters is how the company handles it when it's brought to their attention, and Mossberg generally does pretty well making customers happy. I think shipping the shotgun back to the factory is your best bet rather than taking it to a 'smith yourself, unless they're a factory approved repair facility. There may not be much to the problem but whatever it is, they need to see it. That way if the problem persists or recurs, you're on the record with it from the getgo.
Hope they get it sorted out for you, one of the few shotguns I ever bought new in the box was a Mossberg combo like the one you describe. I used it off and on for a few years with zero problems. I loaned it (and a 1911A1, and my spare Seiko dive watch) to a good friend who had sold literally everything he owned to pay med school bills, including his guns. Hey, what are friends for?