Forgive the cheeky title, but I couldn't resist. I was puzzled at the rejection of my solution when presented with the following Test case:
"yo! Bottoms Up, u.S. Motto, boy!"
which is apparently expected to output:
"Yo! Bottoms up, U.S. Motto, boy!"
My own solution switched the location of the two Y's - which fails to pass the test case.
A quick google lead me to find that despite my own schooling, teaching Y as a vowel, it can also be regarded as a consonant. Given this somewhat broad ambiguity, I think the question should be updated to either state that Y is considered a consonant, or specify exactly which letters are considered to be vowels.