whirr vs let out

whirr is a noun but let out is not a noun.

Word	Noun	Adjective	Verb	Adverb
whirr	Yes	No	Yes	No
let out	No	No	Yes	No

As verbs, let out is a hypernym of whirr; that is, let out is a word with a broader meaning than whirr:

Other hypernyms of whirr include emit, let loose, utter.

whirr (noun)	let out (noun)
sound of something in rapid motion

whirr (verb)	let out (verb)
make a vibrant sound, as of some birds	make (clothes) larger
make a soft swishing sound	make known to the public information that was previously known only to a few people or that was meant to be kept a secret
	express audibly; utter sounds (not necessarily words)
	bring out of a specific state