Well, what do you know (cuh-no)?
Recently, my mother-in-law was reading an Amanda Pig book with my daughter. Anna paused at the word "know," and my mother-in-law laughingly said, "Oh, that word is /cuh-no/!" — making a joke by suggesting that the <k> in the word is actually voiced, or articulated. Anna thought that was very funny, and proceeded to find and read several more examples within the book ("cuh-nee" for knee) ("cuh-nocked" for knocked). It turned into a sort of cute word search.
So, what is the origin of the <k> in the <kn> cluster? According to Richard Venezky's book The American Way of Spelling
(a good book for those interested in the structure and origins of American English orthography), the <k> was little used in Old English, and some time in the middle of the 17th century, /kn/ was leveled to /n/. And there you have it. You "cuh-no?"