Why are certain combinations of sound more “pleasing” than others?

It relates to the shape of your throat, which it is genetic. Martial artists study such things. They teach a yell they call "kiai". The Japanese throat renders that something like "eh-ee" and the Japanese language has a lot of words made only of vowels. The American throat makes a yell that sounds like "heeya" or "hooie" because of the different shape, and Americans do not like words with only vowels.