Better sound on rainy days?

Yes, it does seem that way sometimes and I don't know if it is actually true or a psychological phenomenon.

I do hear all the frogs singing along to my music when it rains. Sort of an enhanced surround sound. I wonder what the frogs are doing in the 360 days it does not rain in my area.

I've been thinking about this too! I can't say for sure if the sound is better or not when it's raining, but it does seem a little different. In my house I can hear the rain so it adds a sort of white noise to the background. I find I have the volume turned up a little higher when it's raining. Technically a speaker should be more efficient at generating sound if the air is cold and dry and the air pressure is high. How audible that is at naturally occurring extremes and whether it sounds better or worse as a result I don't know. Maybe there's some research on it. How the weather effects us physically might have a larger effect on our subjective evaluation of sound quality than any change in the actual signal reaching our ears.