Air Handler making noises ?

[bigdog]

My HVAC Air Handler making noises ? Heat comes on, and starts blowing warm air through ductwork, but when furnace shuts down, the Air Handler makes a loud 'clunk' the shuts off. Furnace to the best of my knowledge is acting as it should.

System is a gas (natural gas) fired furnace, and mounted in the garage. The Air Handler is located, in the attic above a bedroom closet

I'm saying the sound is coming from the Air Handler, because I can hear it shut off in the bedroom closet ceiling, I'm not what else it could be ?

Thanks for your feedback, much appreciated !