Possible Clues:

• Above this point one may listen in to the sound of what's said
• Words after a loud whistle
• "Where are you?" response
• "Psst!" (2 words)
• Shout from an arm waver
• Possible reply to 'Where are you?'
• Attention-getting cry
• Yell from one waving his arms
• 'Psst!' follower, maybe
• "Yoo-hoo!" while waving (2 words)