Reduce sound from a/c in millwork

I do not think you can do much as you air inlet and cool air vents have to be exposed and sound will escape from there.

Putting millwork or anything else which restricts air flow is usually a mistake.

Response,

There is nothing wrong with adding custom millwork (radiator cover) over a radiator. It does make sense to install a metal sleeve from the radiator cover to the new grill.

300 Mercer, did you have an HVAC look at the unit? If they cannot be fixed it might be time to install new ones

Primer, The original poster has PTAC. Millwork is there already. Old ones do make more noise due to age but the new ones also make noise in my experience.

300,

They do make some noise but the newer ones are pretty quite