A non-catastrophic engine failure is going to sound pretty much like normal shutdown on the ramp. A whining sound that becomes less and less as the engine winds down. To the trained ear it would be fairly obvious, especially if both of the engines were winding down. If airborne, the sound of silence would be deafening, except the screaming in the passenger cabin, might be louder.
I was in a plane once and that happened.
The silence WAS deafening. Complete and total silence, plus no one in the cabin was saying a word...
And after a few seconds (20?) both engines powered up again. You then heard a ton of sighs and phews from the passengers.