When I say them out loud, it makes sense like someone in english saying "wuuut" instead of "what?", but that mostly applies to written casual conversation I guess. Anyway is this correct or is it something else?
This site will help you: d.hatena.ne.jp/rhb/20121201/p1– user20624May 10, 2017 at 8:30
1The site will help you: huyuhazimemasita.blog.fc2.com/blog-entry-86.html– user20624May 10, 2017 at 8:37
なぬ is an exclamation to tell surprise, like "No way!" It's probably related to なに, but has lost most of its interrogative nuance. It doesn't sound particularly cute, but a bit old-fashioned and perhaps dialectal, thus mostly used by a modern speaker to add some comical tone rather than a serious surprise.
ぬぬ isn't a meaningful word, instead
a way to spell out grunt, or the sound you utter when you're too shocked to answer anything back. = ぐぬぬ, むむむ, うぐぐ etc.
a way to spell out nasal sound you utter to yourself to show a light doubt. "uh?", "huh?" = ぬ？, ん？, うん？