SW17LS

I don’t know that I would say the “quietest cars ever produced”. There’s a wide variety of measures and results when you test cabin noise, different outlets have dramatically different numbers. I’ve driven the X7 (not the Bentayga) and it’s very quiet, but I wouldn’t say it’s any quieter than an S Class or the LS or an A8 or something like that. All of those cars in that upper echelon are very quiet and it’s hard to say after driving them whether one is quieter than the other.

Raidin

I should add that while the CT rides firm, it won't jolt you over bumps except bad potholes. Tires make a difference.

And while it is quieter than a 3rd gen Prius (haven't tried 4th gens), it's not by much because it doesn't have as much sound-deadening as it should, because Lexus wanted the weight to stay low to keep the fuel economy high.

As far as squeaks and rattles, I have had two minor ones that show up from time to time, but are almost always non-existant. This is well after 500k miles of highway driving.

HOMER350

Riding in my friends v12 bi turbo S-Class that thing is SO quiet. Absurdly quiet like you said. You'd never know riding in it it had anything larger than a 4cyl engine lol. Well, until you strip on it but then its still very quiet. Riding behind it, sounds like a beast.