I can hear the clicking noise from the vent all day - Help

h2o2003

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Here is exactly my problem. It is so annoying. Anyone knows how to fix it? Many thanks.
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nan1

我家有时也有这个声音，好象在晚上经常出现

gray

haunted house???

ceramistpalace

the heat ducts contract and expand thus making that noise

天上明珠

check the furnace

tanrx

感觉是 duct管 热胀冷缩。 请heating的专业人士解答