The sound one makes in response to something peculiar that has just occurred or has just been said. Most often used when irritated. Most often a natural response/reaction.
1) I thought I had a $5 bill in my wallet but it's not here .... hmpf.
And dying in yo' bed many years from now, would ya be willing ta trade all da days from dis here day ta dat fo' one chance, just one chance, ta come back here as young men an' tell our enemies dat dey may take our lives but dey will never take our freedom ... YUB NUB!