So much for 'whisperjet'! To my mind the Sukhoijet is quite noisy being true to Russian form. A recent article in a prominent article reviewed Interjet's Sukhoijet and came to the same conclusion... So let's see how suitable it is once adapted for steep approach and LCY ops.
You'd have to question how Cityjet have not been planning for this, my guess is that they are, and if necessary they'll get some sort off exemption until the new planes are adapted...