>>716414897
I don't exist...

>>714283218
The "Gaster noises" is the background noise of ENTRY NUMBER SEVENTEEN (note the distinction between the noise and Gaster's actual voice chirps speaking over it, which aren't present in Deltarune)
https://www.youtube.com/watch?v=fpneLl7ohUs
Chapter 3 and 4 have basically confirmed the longstanding theory that Gaster's "experiment" was making a Dark Fountain or otherwise experimenting with the Dark Worlds (Ralsei says Dark Worlds are created when you "take away the light that isn't there" (PHOTON READINGS NEGATIVE), and the church hymn outright says "SHADOWS CUTTING DEEP[ER]")
The "music" itself is called "mus_smile" in Undertale, and it's actually the stock laugh effect used by Muffet heavily distorted and slowed down.
The noise playing through your phone in the Dark World can be taken to mean that it's just the "sound of the Dark World," but it could also imply that Kris, like Spamton, is actually connected to a "deeper" or "darker dark" where Gaster may reside (notice that the inside of the Titan, created by making a Dark Fountain within a Dark World, has the same visual pattern as what we see during the intro sequence where Gaster creates our vessel).
The Shelter is known to contain a Dark World, and might have actually been where Gaster's experiment took place. Kris and Dess saw something in there, Dess was lost in the dark and Kris is haunted by A Man. And ENTRY NUMBER SEVENTEEN ends with...
>WHAT DO YOU TWO THINK?

>>528108853
Gaster is Toby Fox's personal "demon"
In the same way that we are "the demon" to Kris, twisting them into a vessel for our will and bringing out their worst impulses, Gaster haunts Toby and his creation, embodying all of Toby's fears.
The man who speaks in hands, who can only connect to others and be understood through a game.
The man who fell into his creation, his life's work cut short and left unfinished, unseen and unspoken, obliterated and forgotten.

>>712516956
The same way you heard about Missingno