Knoking noise when stopping
 

Hi, I have Mazda 6 2003 4 cylinders, a couple days ago I have noticed when stopping I hear knoking noise comming from the rear of the car, I went to my mechanic to check it out he couldn't find anything, he assumed that it could be a wheal bearing from one of the rear wheels. If anybody have experiensed the same problem please advise me what is going on.