The Avanti makes a very distinctive sound, sort of a banshee type screaming noise when it flies over. They're nice, straight forward flying airplanes, and very quiet inside...not at all like they are on the outside. In flight they're quiet enough, in fact, that you can hold a conversation without raising your voice, and people in the cabin can sometimes hear what the crewmembers are saying to each other.
I flew the Avanti for a thousand hours or so, and quite liked the airplane. It's roughly comparable to a King Air 200, but bigger inside, climbs all the way up to and flies comfortably at 41,000', and cruises at 370-395 knots for the same fuel burn as the King Air. It's a goofy looking airplane, like a flying egg with backward engines and three wings (it's a forward wing, not a canard...Piaggio is very big on making that distinction).
Before I started flying the Piaggio I was living near the approach end of a runway at Las Vegas (USA), and would hear the Piaggios coming and going all the time. I could always tell, from inside my apartment, when the Piaggio was coming. It always sounded like it was going to fly in my door, sounded just a little angry. For all their goofiness and funny sound, they perform and function quite well.