In At The Mountains Of Madness the "piping sound" of the shoggoths is transcribed as "tekeli - li". This has always bothered me, as I have no idea how to imagine that sound as piping or whistling. How is "tekeli - li" pronounced (if that is meaningful at all)?
The real answer: Lovecraft did not coin the phrase Tekeli-li!; Poe did, and he gave no specific pronunciation guide.
Of course common reading is what prepared us both to make the interpretation, though Danforth has hinted at queer notions about unsuspected and forbidden sources to which Poe may have had access when writing his Arthur Gordon Pym a century ago. It will be remembered that in that fantastic tale there is a word of unknown but terrible and prodigious significance connected with the antarctic and screamed eternally by the gigantic spectral and snowy birds of that malign region's core. "Tekeli-li! Tekeli-li!" That, I may admit, is exactly what we though we heard conveyed by that sudden sound behind the advancing white mist - that insidious musical piping over a singularly wide range.
And on reading Pym, one indeed finds:
From absolute stupor [the savages] appeared to be, all at once, aroused to the highest pitch of excitement, and rushed wildly about, going to and from a certain point on the beach, with the strangest expressions of mingled horror, rage, and intense curiosity depicted on their countenances, and shouting, at the top of their voices, Tekeli-li! Tekeli-li!
Although the pronunciation of Tekeli-li! is not stated, other than by Poe's own choice of letters, the linguistic Note at the end of Pym says that Tekeli-li! is associated in some way with the concept of the color white.
It would make most sense, according to Poe's spelling, that it should be pronounced teh-KELL-ee-LEE. The way it sounds is a bit more complicated. I imagined it like a mixture between Poggle the Lesser (from Star Wars), Cubert (from the Atari game), a human shriek, and Redeads (from The Legend of Zelda: Ocarina of Time). In my mind it started really low with a sort of "fuzzy" or "filmy" v sort of sound (Poggle the Lesser) for the "Te" syllable. Then it goes up a minor third, if you follow, for "kel". From there it goes up an octave from where it started, but probably about five or six octaves for the first "li". Here is where it sounds like Cubert and it then immediately goes down a half-step for the the final "li". Between the two "li"s is where I imagined the human shriek and Redead cry. It gives this horrifying picture of hazy or shifty vision distorting as the cry is heard. When I imagined it I gagged from the horror.
Pucker your lips like you are about to whistle and then try saying it exactly how it sounds while whistling it out. You get a very eerie and unsettling almost whiporwill type noise. That makes sense as well because in The Dunwich Horror whiporwills are the harbingers of death that come out to steal the soul when it leaves the body.