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?