"ludwig"  wrote:     97 Monte carlo z34.....

The car develops a knocking sound from the engine compartment
after having been driven for 1/2 hour or more, and then only when
I stop at a light or put it in park.  I can even feel the knocking
vibrations through the brake pedal.   The car runs perfectly otherwise,
it idles very well and has good power.  Funny thing too, sometimes
the knocking sound continues for 5 - 10 seconds even after I have
shut off the engine.   The car recently had head gaskets and water
pump changed due to overheating problems.
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There is probably still an overheating problem.    These symptoms can
occur if the radiator is blocked, the heads are cracked, the thermostat
is defective or the thermostat is installed backwards.  The knocking
would be bursts of superheated steam in the engine block or heads.

Wendy & John.
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You might want to start by checking the fuel lines and their
routing.  Sometimes you can get that sort of noise from the
fuel lines if they are grounded out against a component that
travels inside the car.

Ian