Possible Clues:

• Sounds as if one might get over the core, by the sound of it
• Contents of shell
• Edible seed of nut
• There's a rank sound in the middle
• It sounds rank in the middle
• Sound as if the senior soldier is at the heart of things
• Nut centre; sounds like a rank
• Sailors accommodated in part of ship, the centre
• The core of the corps, by the sound of it
• Nut seed