Knocking

This noise generally is heard when the
engine is under load, such as when
accelerating or climbing a hill. While it
often may be caused by a tankful of
inferior gas, ignition knock frequently is a
sign your engine needs attention. It also
can be caused by a build-up of carbon
inside the engine.

Late model cars are equipped with a
knock sensor which "hears" the sound
and makes corrective adjustments. But it
cannot compensate for a severe mal-
function, a condition which can affect
engine performance, even damage the
engine.