2000 Ford Expedition brake problems

I just had the rear breaks changed on my 2000 Ford Expedition. It is now starting to make some interesting noises when I break. When the car comes to a complete stop, it sounds like a 5 gallon water jug is rolling around in back with two “boing” sounds then one more when I start back up. Is this a problem with the new brakes or something else?

Thanks for your help.