Humming
noun
Try singing a nose song. How does it sound? Like humming perhaps?
The readings are both kun'yomi vocab readings, probably because a 鼻 is a body part, and body parts do that to jukugo words. You know 鼻's reading from the kanji (はな) and you know 歌's reading from the vocabulary word 歌 (うた). Combine them together and you have a very nice humming tune and reading, はなうた.
コウイチは、鼻をふくらませながら、鼻歌を歌っていた。
Koichi was humming while making his nose swell.
ビエトは鼻歌まじりで楽しそうに自転車に乗っていました。
Viet was happily riding his bicycle while humming.
アハハ！お前鼻歌下手すぎだっつーの。
LMAO! You are just terrible at humming.