You know those two-word things like: splish splash, tick tock, bing bang, chit chat, dilly dally, ding dong, riff raff, and so on. I don't know what they're called, but I saw something on a news program discussing them and it said the first word in the pair almost always contains an "i". It has something to do with the "i" is easier to say (as to position of mouth and tongue) than other vowels so it comes first.
I thought that was interesting.