The installer that does the building and duct load calculations in
writing and shows them to you is the one I would pick.

Sound level is rated on the db-decibel scale, all manufacturers have
their ratings, they may not be avalaible to you but they are to the
installer. If Scone rating is offered demand the conversion to db since
Scone is not as accurate a rating. Many manufacturer sites publish db
ratings, like Lennox. 1 db makes a difference in what you will hear.