Glad to see the 319s are hotly anticipated in the north. As a long-suffering Thameslink/FCC/Thameslink user I can't wait to see the back of them.
As for being quieter and with less vibration than a 156, have a ride in the carriage with the pantograph and the motor bogies underneath. You'll soon be "enjoying" the "319 Roar" and the "neutral section thud" as well as the "lively ride".
If you move into the carriage containing the (only) toilet, you'll have the pleasure of the air compressor starting up at random times (usually every 4-5 mins) that will shake your fillings out and will soon have every fixture & fitting in the carriage buzzing away with a "delightful" harmonic resonance.
The two end carriages offer by far the best environment, so long as you're not wedged in the middle seat of a three. I can also recommend sitting in the front car of the front unit (if two are coupled together) if you want to enjoy any fresh air from the ecologically-sound air conditioning (hopper window vents). It seems that the aerodynamic properties of the class 319 directs air away from the hopper ventilators when at speed, particularly in the middle carriages, so you don't get a pleasing rush of cooling air over your face during the barbecue summers we've enjoyed recently except in the leading carriage.
The one good thing you'll notice up in the north is the fantastic heating system fitted to the class 319s. Its so good that FCC liked to leave it on all year round in many trains and many of the heating units were so happy in their work, they stayed on all year round in certain carriages, even when the heating was off in the rest of the train. My tip would be to avoid sitting in a window seat, even if you desire a panoramic view of "sunset over Chat Moss" from the 3rd of the window you get to look out of. This is because the floor heating ducts are at a cleverly-designed 45 degree angle right where your feet need to be. This means you'll be getting very friendly with either the person opposite doing the "319 two-step" or the person sitting next to you as you are forced to encroach on their assigned "foot deployment area".
I wish you all well as you strive to make the most of living in the provinces and I take up my spectacular space-age seat in the "smarter than Oxbridge" fully air-conditioned, more comfortable for standing passengers, Siemens Class 700 in the very near future.
The 319s do look shiny in their new livery, but as they say, whilst you can't polish a turd, you can roll it in glitter.