Noise: it's very well insulated from the outside (for the price of the car), above 85mph there is wind noise across the mirrors and once the diesel engine goes above 2600 revs you can hear it. At idle yes you can hear it but it very quiet
Vibration: there is very little vibration through the pedals and steering wheel, I'm impressed by that bit
Harshness: The suspension is not soft, it's quite firm , the advantage of it being it handles very well for such a big car.
Overall, for the price point it's a very comfortable and quiet car, not Audi standard but the same as VW Tiguan (with VW obviously offering sound proof glass as an option which SEAT don't in the UK)