Possible Clues:

• Ding-a-ling or ding-dong
• Turn up for yoga class, did you say? Boo and hiss!
• Word sounded out by the ends of 20-, 35- and 40-Across
• Formation of words sounding like what they mean
• Use of words sounding like what they name
• Thud may be heard, but not on a rug down there?
• Sound-imitating word
• "Buzz" or "pop," e.g
• Word such as "woof"
• Sound words from parent to writer in love no one initially acknowledges