This is a modern cruise ship - not a Dover Calais car ferry. Baja deck is deck 11 - the 'engines' are at least 12 decks below you. Of course there is no noise.
There is certainly no need to worry about engine noise on Baja deck, or any other noise for that matter as there are no public decks close. You may feel the movement of the ship slightly more in this position than you would in the centre of the ship. However all new ships are equipped with stabilisers so unless you hit some really bad weather I think you'll be fine.
My husband and I stayed on the Baja deck last year and it was an excellent choice... no noise, private decks... and although I have gotten sea sick on past cruises , no problem on this deck. We even requested it for this year, but were upgraded.
have a great time...