ac noise

If you have any metal duct work, it could simply be a shift in a metal panel due to a change in air pressure. ^_^

TDD

Probably not; it's likely just the motor contacts closing/opening you're hearing. But, if it's a new installation call and ask...

Since it's new, call the installer/service provider.

Tell them that you have a concern and that you'd like it checked out before something goes bad.

The call should be covered under the warranty. At a minimum you'll have your concern documented in case it gets worse later.

Since most of us have a hard time hearing "clunking sounds" over the internet, and your idea of "slight" might be very different from ours, I suggest that you get a professional to come listen to it.

Fan blade hitting the side.

A *slight* clunking noise on startup and shutdown must be the low voltage holding coil in the contactor doing its job - nothing to worry about. Two pieces of metal clasp together by an electromagnet, as they were designed to do, and make that sound.

------------------------------------- /_/ ((@v@)) NIGHT ():::() OWL VV-VV

What he said seems most probable.

yOU HAVE all MISSED IT. tHE COMPRESSOR UNIT IS RUBBER MOUNTED, AND THE STARTUP TORQUE MAKES IT JUMP IN THE RUBBER MOUNT - MAKING A "CLUNK" - AND WHSN IR SHUTS DOWN ALL THE ROTATING MASS STOPS AT ONCE AGAINST PRESSURE, MAKING IT ROCK IN THE MOUNTS AGAIN - CAUSING A "CLUNK". nOT AT ALL OUT OF THE ORDINARY - PARTICULARLY WITH THE NEW SCROLL COMPRESSORS.

Excuse the mixed caps - I hit the shift lock instead of the shift and I',m too lazy to retype it all.