I would tend to go along with what 3holeover and lomapaseo have posted. The vibration sound and feel may also be influenced by harmonics as 777AV8R pointed out, depending on where you are seated.
There is no influence, one way or the other, caused by the composite fan blades.
The 20 minute stabilization after landing before shutting the engines down certainly helps, but it probably doesn't occur on a regular basis. With a bowed rotor on startup, the LPT area is most affected until things settle in. Additionally, as the rotors start to turn and pick up rpm's, there are a lot of frequencies being crossed which are designed to be outside normal engine operating range (idle through TO thrust). These sounds and vibrations are often transmitted from the engine, through the pylon to the wing and fuselage giving some strange sounds when seated near the engines or wing area. These all go away as the engine approaches idle speed and everything is in sync.