When a jet transport takes to the air the engines sound like they're being flogged to within an inch of their design capabilities.
I know they are throttled back a bit once established in the climb out but when cruising altitude is achieved what settings, compared with climb out , are the engines set to. Can a comparison be made with another form of propulsion? Also, what would the engines sound like if I were positioned at FL370 and it flew by at close proximity? My question is: would they still sound like they do at take off?