Are you talking about the clicking sound? I had a similar sound with mine, and it was the idler arm moving back and forth because my belt had a bad spot on it from being burnt. But you said he checked the belt. Maybe the belt is defective and out of balance. A new belt would be a quick and easy way to rule this out. The other thing could be the transmission housing moving back and forth during agitation. It is normal for there to be a little bit of play against the brake assembly. The video seems to be during the agitation cycle, not the spin cycle.