Possible Clues:

• Very soft-hearted footballer's stone
• Much too small to soundbolder
• Seems one is not only on the beach
• That makes one sound just a little bolder
• One of the Stones appearing worn - affected by the drink?
• It's mainly smoothed out in a Rolling Stones remix
• Footballer collects books of calculus
• Just a little bolder, by the sound of it
• Not for you to be the only one on the beach - that's a little hard
• This makes one sound just a little bolder