Argus Reed Frogs Calling - YouTube - that's a video of some calling at one of our stores a while back. It's noticeable, but not so loud that you'll regret having them in your home. They are on small crickets - as birdsflybackwards noted, they need something bigger/more substantial than fruit flies. We offer ours small (1/4") size crickets, although I don't doubt in the slightest that they'd take something larger.
-Jen