4 cylinder engines sound dreary because there are no overlapping ignition strokes. Whereas in the larger engines, there is always a secondary ignition about to occur on the same upward stroke.... which means the sound they produce is much more pleasing to the ear, and hence PREMIUM.
Due to the 4 cylinder only policy, it means new Volvo's do not have premium engines, which is a real shame because ultimately Volvo needs as many USP's as possible...
4 cylinder engine:
5 cylinder engine: