Possible Clues:

• Making moos
• Line outstanding, calling from Jersey or Guernsey
• Mooing
• Cow sounds
• What's heard from Gray's herd
• By the sound of it, way Gray's herd not on the up-and-up, perhaps?
• Row of cows travelling not so fast when leaderless
• Being left in debt sounds familiar in the countryside
• Gray's herd might leave a pound unpaid as it winds slowly