Speak Incoherently; Make Noise Like a Brook
Puzzle 11 of Millennial Words Hard Pack
Question is: Speak Incoherently; Make Noise Like a Brook
and the answer is: BABBLE
Word Meaning:
BABBLE — (intransitive) To utter words indistinctly or unintelligibly; to utter inarticulate sounds
Definitions from Wiktionary.