Is the huge white metal grille on a ceiling called a "cassette AC". Is it supposed to be noisy?
That's the return air grille, where the AC's air handler sucks up air to cool that it pushes through the ceiling registers in the other rooms. Central return systems are inherently noisy, but good duct design can alleviate this to a certain extent as can using a smaller blower motor if the ductwork was done well enough that the reduced airflow speed doesn't result in worse air delivery.

Your bigger problem is the fact that your air conditioner is in the attic, where it will get to be like 140 degrees. I bet every time it kicks on, all the rooms get blasted with a slug of hot air for a few seconds, right?