Usually your only indication they are operating is the mud being churned up. With bow thrusters and either stern thrusters/pods, the ship can move sideways or pivot. They are also handy to offset an onshore or offshore wind.
We had a forward suite on the Regal Empress years ago and the bow thruster sounded like the anchor being let go. The ship's draft was so deep, she was a converted (sort of) ocean liner, we had to stay so far offshore at the various ports that we couldn't anchor. The ship had to constantly maneuver to maintain any semblance of position and we had to listen to the racket all day.
So much for bow thrusters.