Pronunciation: the verb "use" versus the noun "use"

Solution 1:

I don't know about regional or dialect changes, but "use" has only one pronunciation for what concerns the "vowel" sound in it.

The last consonant sound changes, being [s] and [z].

It's [juːs] when it's a noun and [juːz] when it's a verb, becoming [ju:st] when we have the construction "used t-o".

Solution 2:

The real difference between these pronunciations is that use (the noun) is pronounced with an /s/ and use (the verb) is pronounced with an /z/ (except in the construction used to). In American English, vowels that are followed by a voiced consonant are longer than those followed by an unvoiced consonant (see this wikipedia page), and this is the source of the length difference you are noticing.