From The Collaborative International Dictionary of English v.0.48:
Ping \Ping\, n. [Probably of imitative origin.]
The sound made by a bullet in striking a solid object or in
passing through the air.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Ping \Ping\, v. i. [imp. & p. p. Pinged; p. pr. & vb. n.
Pinging.]
To make the sound called ping.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
backfire \backfire\, back fire \back fire\
1. A fire started ahead of a forest or prairie fire to burn
only against the wind, so that when the two fires meet
both must go out for lack of fuel.
[Webster 1913 Suppl.]
2.
(a) A premature explosion in the cylinder of a gas or oil
engine during the exhaust or the compression stroke,
tending to drive the piston in a direction reverse to
that in which it should travel; also called a knock
or ping.
(b) an explosion in the exhaust passages of an internal
combustion engine.
[Webster 1913 Suppl. +PJC] Backfire