Hi! Dev here!
To give some clarification:
We do have a little beeping sound that triggers when enemies being highlighted. So if you are highlighting 3 enemies you will hear 3 beeps or sound ques, one for each as they gets highlighted. This is to make it so that if you pick up one beep you know that one enemy is highlighted. Several beeps you know that there is more the one. No beeps, no enemies, etc.
This also applies to other allies if you choose the talent Bio optic targeting. Then your allies in coherency also see outlines and they will also hear beeps for each enemy highlighted. So even if you don’t trigger your ability, another veteran in you strike team might trigger theirs (with the talent) and cause you to see outlines and hear beeps.
All the 3 level 30 talents for sharpshoter also makes the outline refresh if you kill an outlined enemy. This will keep the outlines of the enemies that is currently outline AND outline any new enemies not already outlined that have walked into ranged or being spawned. The new outlines will also trigger a beep.
So to sum up: one beep for when an enemy gets highlighted be it from your ability or an ally.