I recently purchased a condo on the top floor of a midrise building. The main return air handler is situated in the living room... unattractive but mainly very noisy! A conversation stopper... or you have to yell when unit is working. Is there any possible way, short of major surgery, to make this unit quieter? Why it is situated where is defies common sense. What can I do?

Likely there is a problem with it. Have you changed the air filter? From there, go to the seller and complain. The seller is responcible to deliver all systems in good working order.

Have you checked other similar units in the building? If they are quieter, likely yours could be too.