I own a Piaggio 300cc Scooter, not called a Vespa because it is one of the big wheel variants (similar to Honda SH line) but it has the same engine as the Vespa 300GTS.

It is not at all noisy unless I rev it high, which I try to avoid doing most of the time. It is not loud like for instance a Yamaha T-Max, not helped by it attracting mostly complete retards.

Obviously there are always dumb people mounting akrapovic or other noisy aftermarket exhausts on any bike brand but it is also the same with cars.