Here’s a review of the phrase/character from Phineas and Ferb :
"Meep" is the only word spoken by an adorable, spherical, orange alien named Meap (often misspelled as "Meep" due to pronunciation). He appears in the episode "The Chronicles of Meap" (Season 2) and later returns in "Meapless in Seattle." Meap is a intergalactic agent from the planet Meap, and his high-pitched "meep" conveys everything from joy to urgency. meep phineas and ferb