With the exact count of repeats of tʼ and ! being variable, the lateral click being optional, and the entire dento-alveolar bit being more of a smooth sequence descending in pitch, decreasing in tempo, and backward in location.
Sure, none of those are vowels, but that hasn't stopped anyone else, including the OP, so fight me.
Location:Setting His Controls For The Heart Of The Sun
I'll have to go with "Eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee" since "Eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeexactly!" was my catch phrase for a while. I change my catch phrase every couple of months or so, but I ALWAYS have one.