있는다: formal non-polite non-past form of 있다.
The other non-past forms are:
• 있어 (informal non-polite)
• 있어요 (informal polite)
• 있습니다 (formal polite)
The sentence above is NOT a correct one.
It must be like this: 우리는 소리를 듣고 있다. In Standard Korean '있는다' is NEVER used.
Removed!