I was telling a newbie friend of mine about this and those who were in the server went crazy with the information, I previously thought it was common knowledge. I figured I would share it with you all.
When you arrive at a capture point and begin to wind the counter down you will hear a chime equivalent to what I imagine the flag sounds like when its coming down the metal pole. You will ONLY hear this chime if no enemy players are in the area you are capturing.
For instance, if you and a squad mate move onto "A" to capture it, as the opposing team currently owns it. If the two of you are uncontested you will hear the audio chime I explained as the flag winds down the pole and you come closer to capturing the objective.
In contrast if the same two people head to capture "A" and arrive but there is a camper hidden on the flag, yet is outnumbered on the capture point you will notice the flag winding down just the same just there will be no chime, no beeping as you capture. This is a sign that although you may not see the enemy, there is at least one combatant currently contesting the area you are capturing.
I hope this helps!!
TL;DR: If you are capturing an objective in conquest and hear the "beeping" of the flag you are alone, If you do not hear the beep you've got tangos in your AO.