D&D 5E Woo Hoo, Invisibility Stopped It's Downward Spiral

[KarinsDad]

If someone makes noises, you have no disadvantage on perception checks.

Yeah, I shouldn't have said "made noise", but at the time, I couldn't think of a way that the NPC would know that the PC is there. Let's use a slightly different example. NPC 1 does not spot the PC, but NPC 2 does (and NPC 2 is some distance away, so he cannot point to the exact location). NPC 2 yells out to NPC 1 that the PC is in that hedge over there.

NPC 1 was walking down the trail and got a Passive Perception vs. Stealth and failed.

NPC 2 then alerts NPC 1 of the danger.

NPC 1 now gets a normal Perception at Disadvantage vs. Stealth for lightly obscured.

If someone makes a noise and is still then (does not move) The observer may have advantage to detect a creature in light obscurement (cancelling disadvantage), but only if that creature has an ability to hide in plain sight at all (like the woodelf).

How exactly would someone get advantage on a perception roll in any circumstance without a direct rule for it?