Then came more firing, and the sharp plonk of bullets as they struck the building were plainly heard by the watchers.
"The Son of his Father"
Ridgwell Cullum
When things were quiet again I distinctly heard plonk, plonk, plonk, the sound made by hand grenades, rising from the lower ground in front, this was soon followed by the fainter cracking of a machine gun and a brilliant Verey light, which I concluded was from three to four miles away.
"'Brother Bosch', an Airman's Escape from Germany"
Gerald Featherstone Knight
Something would go plonk when the trigger was pulled on an empty chamber, so I did some dry practice at the crests of waves.
"Four-Day Planet"
Henry Beam Piper