I just moved into a new place and it's the first I've ever had central air. The furnace is a Heil single stage unit. When the AC has been running and turns off, either manually or automatically by the thermostat, the blower shuts off and everything seems fine. However, then about an hour or after it's been off, the furnace makes a loud 'whir' sound that lasts two or three seconds and then cuts off. Sometimes it'll happen one or two times after the first time, about 5 minutes apart. Again, this only seems like when the AC has been running. It seems like a distinct 'whir' sound and not like when the blower turns on.
Is this normal? I'm not used to a central AC system. If it's normal, what's it doing? Thanks.