Gyurururu...

Gyurururu... is the noise made by Perry the Platypus of Phineas and Ferb. Dee Bradley Baker makes this noise, and his "understudy" is Thomas Sangster, who also voices Ferb.

It's official spelling was revealed in the Phineas and Ferb video game for the Nintendo DS. When you approach Perry, he says "Gyurururu..." and the game asks if you want to save.