Breelan used to not make a peep... like ever! She was a rescue, and we thought that something had actually happened to her vocal chords, because sometimes it even looked like she was trying to bark, but couldn't.
Then one day we were teaching Gordy to shake (like whole body shake, not just a paw) and saying "ShakeShakeShake!!!" really quickly seemed to be motivating him. Well... Breelan barked. So, we started making that noise to get her to bark. Changed it to "SpeakSpeakSpeak!!" which worked too, and we just branched off from there. What ended up happening, is that speak was her default trick when she wasn't sure what to do. So... we taught her "Shh!" We'd get her to speak, then we would say "Shh!" and give a treat when she stopped barking. Now if she gets excited during training and starts to bark we just say "Shh!" and she stops barking, we give a treat, and we continue. She just thinks it's another trick.