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In the morning when our heat pump is turning on to start heating the house for the morning, I hear repeated thumping that kind of sounds like sheet metal rumbling. This continues periodically for a while and then seems to go away later in the day.

Is this due to the emergency heat kicking in to supplement the heat from the heat pump? Is this the heating ducts rumbling? Should I be concerned about this noise (other than the fact that it wakes me up)?

Are there more details I can provide to help clarify the issue?

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up vote 2 down vote accepted

Sounds like the ducts expanding and popping against themselves and the wood framing as they heat up. If that's the case, it's nothing to be concerned of since they are designed to expand/contract.

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Is there any way to mitigate the sound? – WilliamKF Dec 10 '11 at 17:02
@WilliamKF sorry for the late reply, just noticed this. The only fix I know of is to put a material between the wood and metal that will allow the duct to slide smoothly. But since it's likely inaccessible (behind a wall), most people just live with the sound. – BMitch Jul 31 '12 at 21:01

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