One of the things I remember most vibrantly about flying R was the noise in the front of the plane. It was not the roar of engines, but instead the sound of rushing air. Imagine the worst windstorm you've ever head from inside a building and that's sort of how I remember the sound. I've read that it sounded like a 'sizzle', but I don't recall it that way.

Anyway, it does not answer the question pertaining to the engines, but for the records, it was moderately noisy.