Goblin say Psshkoh

[Shikiseki]

I always read it as it's some kind of catchphrase like kupo... pshkoohhhhhhh
IDK sounds lot cuter than darth vader breathing (although that kinda is funny too)

[Catapult]

Request: Next Eorzean census, tell us how many goblin treasure hunters never made it home.

Because, psshkoh, nastythings uplanders manymake.

[MiniPrinny]

It's just to let you know that their voice (and the sound of them breathing) is distorted from their masks. If anything, we should be asking if they're canine considering that they bark at us.

[Lusavari]

You know that sound of static that comes over a radio when you push the talk button? That's what it is.

[Alice_89th]

They may have shared genetic traits in regards for them needing their masks, but I wouldn't go that far.
But yeah, it's the sound of them breathing.

The Vath quests deal with the Gobbies using herbs in their masks, but I don't recall anything about them really needing the masks to breathe (just that it is really rude to try and see underneath).

[ADVSS]

apparently they have strong sense of smell in which the masks, filled with aromatic herbs prevents them from having to smell uplanders b.o. but iirc the older versions of goblins. imps/etc had very long roxanne-like noses so i can only assume coupled with the masks is how they look without a mask. would love to see an unmasked goblin just once in game though someday.

[Zohar_Lahar]

The Vath quests deal with the Gobbies using herbs in their masks, but I don't recall anything about them really needing the masks to breathe (just that it is really rude to try and see underneath).

One of the FATEs in the Hinterlands imply the masks contain filters for impurities (e.g. allergens).

[Aryalandi]

Goblins in Final Fantasy XI (same design) wear masks for much the same reason, to filter out the smell of things above ground (most are miners) because they find it unpleasant. They fill their masks with a type of herb that they like in order to make it easier for them to breathe normally.

so yes, the sound is literally "darth vader" breathing. Because we upworlders and all of our above ground things offend their delicate and refined noses