In a Reddit thread about how to spell lightsaber sounds (Star Wars), user Takai_Sensei posts an interesting comment about the difference between onomatopoeic and echomimetic:
"Snap-hiss" is what we would think of as a standard onomatopoeia: a word that represents and imitates a sound. This is in the same category as "meow" and "whoosh." They conform to some standard spelling rules and are used grammatically like words are.
But things like "bwwwwoooggzzhhheee" and "BIZZOWWWWww," while still onomatopoeic, are more on the echomimetic side of things. This is more like using letters to transcribe exactly what you hear as close as possible.
Both are "onomatopoeia," sound words, but they are slightly different.