Yes, STRIDENT is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, R 1, I 1, D 2, E 1, N 1, T 1.

Is it a valid word?

STRIDENT is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

conspicuously and offensively loud; given to vehement outcry
of speech sounds produced by forcing air through a constricted passage (as `f', `s', `z', or `th' in both `thin' and `then')
being sharply insistent on being heard
unpleasantly loud and harsh