I had just gone up the top of a mountain in the extreme hills biome when it started to snow. As I moved down the mountain the snow stopped and the rain started. However, for those four blocks which were showing rain particles, I was unable to hear the rain. However, upon walking back up the hill I can hear it fine. These extreme hills were generated in 1.4.x.
You cannot hear rain here because there are no rain particles (they look like scattering drops on a surface) for this biome. Anyway, rainy weather must create noisy particles if it is raining here (but not snowing). But now rain sprites (visible rain drops texture from sky) and rain particles are separated. Altitude rain/snow feature is introduced for rain sprites only, rain particles stayed depend on biome.