Rhymes with stirrup

The oldest, who will be at the barn twice a week over the summer, wants to know. "Momma, what's the word for the noise? The one you make with your teeth and tongue and cheek? To make the horse move."

I have to think for a bit, but I finally remember.

chirrup
noun
1. A series of chirps.
2. A series of clucks or clicking sounds, such as those made to urge on a horse.
"chirrup." The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. Answers.com 11 Jun. 2006. http://www.answers.com/topic/chirrup