While there is a general rule to use "an" before a word starting with a vowel, the exceptions tend to create confusion. For words starting with a "u" (not "an u"), the choice depends on how the word is pronounced. If it's pronounced with a short "u," as in "uncle" or "uncertain," the general rule applies. But if it's pronounced with a long "u" (the diphthong: "yoo") as in "uniform" or "university" (or, in this specific case, "Ute"), the "y" sound is treated as a consonant and the correct article is "a."

The issue gets even messier (and uncertain) when dealing with words beginning with an "h." Even though "h" is a consonant, the question of whether it's "correct" to say "an historic event" or "a historic event," for example, gets different people worked up arguing that one or the other is "correct." I blame William the Conqueror.