lol ack ack...the answer is yes, i a manner of speaking...anything that covers your ears muffles external sounds...as you can see in the pics (wwii german pilot helmet), the radio headphones built in to the helmet covered the ears:

of course in a bomber like the b-17, aside from the engine noise, the pilot would not be able to hear the bomb bay doors with his helmet on.
the term "noise cancelling" actually refers to modern microphones...where background noises are electronically filtered, not the speakers that cover your ears.