What does the second の mean in this sentence?
Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.Sign up to join this community
The second の is a nominalizing の.
It turns the phrase 「すっごいレンジの音がしてる」 into a noun so the grammar 「Nが気になる」 can be used to mean "N is on one's mind" or a similar meaning.
Another example of this usage of の is:
(I) dislike playing video games.