That is the unfortunate vocal noise - a click or thump - that occurs when you "hammer" the syllable immediately after the breath. It sounds pretty awful.
O be joyful in the Lord, all ye lands:
SERVE the Lord with gladness, and come before his presence with a psalm.
People tend to clobber "Serve" - to a lesser extent they will also hammer "all" and "come" and the second syllable of "presence".
. . . . sorry , just got out of 2 1/2 hours of choir practice.
2.5 hours of choir practice, eh? I sing tenor myself. What are you singing for Holy Week?