This discussion has just come in a recent session of our, and I was hoping to have someone else weigh in! One of our players is a Protector Aasimar, and was trying to use their Radiant Soul feature to fly up to a window during a stealth mission. They had already cast Invisibility on self, so the obvious radiant glow wasn't a problem, but the point of contention came up with discussing if the wings made noise during flight. 

Overall it came down to whether flight is granted by physics (physical wings flapping to generate lift), or magic (e.g. the "Fly" spell, which grants the recipient Superman-esque flying with no external motion). The feature description says they are "incorporeal wings", but the DM eventually ruled that since the fly speed is accompanied by the manifesting of wings, even if they are incorporeal, then they must flap, and thus must make some noise. 

Anyone have this issue come up, or any thoughts to weigh-in?

Wings imply that they move in order to gain flight - whether they are purely physics or magical shouldn't make much difference. Wings especially move when you gain altitude.

I would require a stealth roll if there was a chance of hearing the wings.

Note that an invisible character carrying a torch still sheds light, you just can't see the actual torch which is shedding light.

I would pick a third option "the wings work according to the rules for how they work" but in reality, it would have to be the supernatural "magic" nature of the world (which is different than the magic of spells and magic items) that would cause them to work.  "Realistic" wings to lift a medium humanoid would require either the humanoid be extremely small/light, or the wings be huge,  neither of which really fit with the descriptions of the creature.

i would rule the wings "flap" to create lift, and would displace air (causing noise), but they are magical (read: supernatural), so a different DM may rule otherwise if the rules do not specifically say one way or the other.

Since Protector Aasimar are the only ones, officially, that can fly.

From the Radiant Soul feature, emphasis mine: "Starting at 3rd level, you can use your action to unleash the divine energy within yourself, causing your eyes to glimmer and two luminous, incorporeal wings to sprout from your back."

The flight is magical and wings don't make any noise at all. They're not physical so cannot physically interact with the air at all.

Since the wings are in an incorporeal form would that qualify as “Magic” thus negating the negative aspects of flying mechanics in the DMG?

Quote from Wizard_Remuel >>

"incorporeal wings"

 Do not move air. Sound is air moving. Incorporeal wings to not make sound. Except if they do so by magic. Personally I'd go by rule of cool: If you're swooping in to smite the faces of the unrighteous, the wings will *WHOOSH* dramatically. But if you're landing behind an unsuspecting evildoer, they will be as quiet as an owl hunting a mouse.

Quote from Littlebighorn89 >>

Since the wings are in an incorporeal form would that qualify as “Magic” thus negating the negative aspects of flying mechanics in the DMG?

 No, because the ability doesn't say they're magical.

I assume being  incorporeal wings that they don't make noise when flapping in and of itself, but the character may still produce sound when flying this way due to gears moving etc.. so i'd still require a Dexterity (Stealth) checks when attempting to move silently as it doesn't specifically say it auto succeed or grant advantage when doing so like Boots of Elvenkind do for exemple.

I say it depends on the nature of the flight. Are the wings what allow you to fly, or are they just an aesthetic effect? Based on the lack of hover speed, I’m guessing it is the former. If you are using the pumping motion of the wings to fly, that means the wings are moving the air. Thus vibration will occur and sound will be produced. If you are gliding down to a location, you may be able to land quietly via a successful stealth check, possibly with disadvantage.

The “magic” of the wings is that they are summoned. Other than that… they are ordinary wings.

Quote from DragonRiderHN >>

I say it depends on the nature of the flight. Are the wings what allow you to fly, or are they just an aesthetic effect? Based on the lack of hover speed, I’m guessing it is the former. If you are using the pumping motion of the wings to fly, that means the wings are moving the air. Thus vibration will occur and sound will be produced. If you are gliding down to a location, you may be able to land quietly via a successful stealth check, possibly with disadvantage.

The “magic” of the wings is that they are summoned. Other than that… they are ordinary wings.

 
And here somebody who doesn't know what incorporeal means.

Well, regardless of if the wings move air, a human-sized body moving through the air at speed would still generate a fairly noticeable disturbance, if only from the displaced air.

So, at this point, I'm noticing that in OP's post, there's no mention of a stealth roll, just that the Aasimar is invisible. I feel like all of this could easily be explained by the DM just asking for a stealth roll... if the player rolls well, they manage to get to the point they're trying to reach without making noise. If they roll poorly, then they make noise somehow... whether it's the wings flapping, knocking down a loose brick... whatever. At the very least they're still invisible so they could try and do something if they get heard.

Quote from Cyb3rM1nd >>

Quote from DragonRiderHN >>

I say it depends on the nature of the flight. Are the wings what allow you to fly, or are they just an aesthetic effect? Based on the lack of hover speed, I’m guessing it is the former. If you are using the pumping motion of the wings to fly, that means the wings are moving the air. Thus vibration will occur and sound will be produced. If you are gliding down to a location, you may be able to land quietly via a successful stealth check, possibly with disadvantage.

The “magic” of the wings is that they are summoned. Other than that… they are ordinary wings.

 
And here somebody who doesn't know what incorporeal means.

 So, quick question: In your games do protecter aasimar just levitate around with fake wings that exist for no reason? From what I understand the word “incorporeal” in the way it is used here means “ghostly” or “translucent”, or in other words they don’t look like they’re made of matter, yet the manifesting of these wings allows for a non-hover flying speed such as that possessed by creatures who use the flapping of wings to fly. Who knows, maybe I’m wrong and it’s like the flight of modeons where they are somehow able to fly with tiny wings and bodies made entirely of metal? After all, magic.

Either way, landing quietly requires Stealth, whether you are flying or not.

Theoretically, if Protecter Aasimar fly without the wings, then the wings have absolutely no purpose for existing. Typically stuff exist for a reason, even with magic. Perhaps the flapping of the wings functions as a Somatic component for the flight effect.

Somatic are spell components and nothing else.

Also while the Radiant Soul trait is supernatural it's not magical according to official ruling from Sage Advice Compendium below:

Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?

• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?

• Is it a spell attack?

• Is it fueled by the use of spell slots?

• Does its description say it’s magical?

If your answer to any of those questions is yes, the feature is magical.

Quote from DragonRiderHN >>

Quote from Cyb3rM1nd >>

Quote from DragonRiderHN >>

I say it depends on the nature of the flight. Are the wings what allow you to fly, or are they just an aesthetic effect? Based on the lack of hover speed, I’m guessing it is the former. If you are using the pumping motion of the wings to fly, that means the wings are moving the air. Thus vibration will occur and sound will be produced. If you are gliding down to a location, you may be able to land quietly via a successful stealth check, possibly with disadvantage.

The “magic” of the wings is that they are summoned. Other than that… they are ordinary wings.

 
And here somebody who doesn't know what incorporeal means.

 So, quick question: In your games do protecter aasimar just levitate around with fake wings that exist for no reason? From what I understand the word “incorporeal” in the way it is used here means “ghostly” or “translucent”, or in other words they don’t look like they’re made of matter, yet the manifesting of these wings allows for a non-hover flying speed such as that possessed by creatures who use the flapping of wings to fly. Who knows, maybe I’m wrong and it’s like the flight of modeons where they are somehow able to fly with tiny wings and bodies made entirely of metal? After all, magic.

Either way, landing quietly requires Stealth, whether you are flying or not.

 
In my games I dont think about it or give a shit. Its a game, not a life simulator.

Doesn't matter if walking, running, flying, backflipping, earth gliding, dancing, wallclimbing, or throwing it back. If peeps wanting to be quiet, they roll stealth. If they don't care, they don't roll and can be heard. Simples.