Possible Clues:

• Distinctive sound coming from pub, I note
• Call yours truly in gym about perfect start to morning
• Perhaps mobile, with its case, producing little sound
• Make call to the writer in linguistics unit
• I want to hear from you in the linguistics unit
• Ring this person found in sound unit
• Page with note about Polish sound
• "I'll wait for your call"
• Smallest unit of sound which is significant in a language
• 'Sh,' 'th' or 'ou'