grammaticality - Is it "a user" or "an user"

Since user starts with a vowel shouldn't we use "an" ? I've seen many cases of using "a" .

Answer

From Amerenglish:

"An" goes before all words that begin with vowels:

With two exceptions:

When "u" makes the same sound as the "y" in you, or "o" makes the same sound as "w" in won, then "a" is used:

• a union


• a united front


• a unicorn


• a used napkin


• a U.S. ship



• a one-legged man