edmontondown 发表于 2013-1-2 23:56 ) ]% F" w( ?9 Q0 y6 M& Ryes, may have something fell down on the other end of the hood vent
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At the other end(outside) of the vent duct, there is usually a metal cover for the opening, it can swing up and down and if it is a windy day, it will be blown swinging, thus making a kind of banging noise.