Is that really a concern for them? I was under the impression that with the advent of nuclear subs, "quiet" kind of went out the window. I took a tour of a Canadian sub once (diesel electric), and they explained to me that while diesel electric is older, less efficient tech, it nevertheless has the advantage of being able to operate truly silently. They can kill the engine and run on battery power. (Actually, while submerged, they HAVE to run on battery power, because the diesel engines can only run while the sub is surfaced, as it needs air intake).
Nuclear subs, on the other hand, cannot simply shut down the reactor, thus there is a constant, unavoidable noise being perpetually generated. Under those circumstances, I'm not sure they'd be too concerned about the noise involved in blowing a few pounds of sh*t into the ocean.