As an NES but not an English phonetics specialist:
I'd not specifically noticed it before, but "t" followed by the long vowel "u" could sound as though it's pronounced "chew...". It also occurs in words such as "tuna (fish)", "Tunisia", "tunes" etc.
If "t" is followed by a short "u" it's pronounced as in "tummy".
I would, however, defer to the phonetics specialists on the forum for a definitive answer.