The difference a vowel makes

Clink is the sound of two flutes of Champagne, kissing in midair.  Unlike like other celebratory noises (the spew of a kazoo, the blare of a goal alarm, "OMYGODYES!", etc.) a clink comports itself with class and refinement. It does not strain to be heard, nor insist on its presence. Like the dignified lift of a conductor's baton, a clink is subtle but commanding. A clink is to be respected.

Clunk, on the other hand, doesn't get the same respect.  It's a soiled workboot landing on a hardwood floor. Or the protest of a second-hand credenza, jostled in a stairwell by sweaty movers.  It's the bellow of a sedan, who's trunk refuses to admit another suitcase. It's the sound of defeat, really. And that's a surprising truth for those who expect otherwise of defeat: perhaps an anguished moan or bawl. It is merely a tuneless clunk; a pair of unmanned rowboats thudding in a foggy, waveless sound.

Clank is more feared than respected. Like a wrench thrown across a noisy garage or construction site, one keeps an eye out for clank. It is a neighbourhood bully, dragging a rusting pipe against the inner city asphalt. Clank is the sound of straining machinery and thus the annoying tune of Progress; the soundtrack by which we leave that we know and love. Clank is a heavy hammer against metal that glows like an oncoming future. Clank is musical theatre with chains, it is religion with cast iron, it is proof of an emptied oil barrel's ultimate demise as it is lost into a deep, deep canyon.

Clonk is specifically the sound of getting hit in the skull with a rubber or wooden mallet.

And clenk, like the sound of astonished eyes, is no sound at all.