I tried the JuceDemo, it compiles fine, but there is no sound (with the FilePlayback and MIDI i/o sections for example).
I've tried with the 3.1.1 release and with the latest commit on github.
My configuration :
Mac Mini (Mid 2011)
OSX Yosemite 10.10.1
I saw Audio issues in this forum but it talks about compiling problems, it's not my case since I can run the demo.
I don't know what to check. I've tried OpenFrameworks sound examples and I have sound.