talk vs sound out

talk is a noun but sound out is not a noun.

Word	Noun	Adjective	Verb	Adverb
talk	Yes	No	Yes	No
sound out	No	No	Yes	No

talk (noun)	sound out (noun)
the act of giving a talk to an audience
an exchange of ideas via conversation
idle gossip or rumor
a speech that is open to the public
discussion; (`talk about' is a less formal alternative for `discussion of')

talk (verb)	sound out (verb)
express in speech	try to learn someone's opinions and intentions
exchange thoughts; talk with	speak, pronounce, or utter in a certain way
reveal information
use language
deliver a lecture or talk
divulge confidential information or secrets