edmontondown 发表于 2013-1-2 23:56 ) b5 A0 K: h/ T& ^' X! wyes, may have something fell down on the other end of the hood vent
4 t# \, @) f/ h, }& Y1 g! @- YAt 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.