I have a 2001 nissan Altima gxe. When I turn off the car and am walking away, it sounds like there are lots of little pebbles bouncing around somewhere near the front of the car. I haven’t seen anything under the hood, and the car isn’t moving anyway. Could this be some normal settling of the engine, or is something wrong?
While it shouldn’t sound like pebbles rattling around, my first guess is going to be that you may be hearing the electric cooling fan(s) running, which is normal (the fan operation is normal, the sound of pebbles from the fans is not normal). When you lift the hood, can you see the cooling fan(s) operating while you hear this noise?
Another possibility–which is a remote possibility–is that the engine might be “dieseling”, which is a condition where the engine continues to run without spark, due to the presence of hot carbon in the cylinders which is igniting residual gasoline. Since the gas is igniting at an uneven rate, the accompanying noise is like a badly running engine, with much vibration. That being said, this situation should not exist on a modern fuel-injected car with an electric fuel pump, but…
If the car is dieseling, the easiest way to tell if this is happening is to go to the exhaust pipe and to do a “sniff” test. If the engine is dieseling, the exhaust will have a really acrid, NASTY smell. If it is dieseling, it needs to be seen by a mechanic a.s.a.p. before valve and/or piston damage takes place.
I am sure that other members of this board will have other possibilities for you to pursue, in addition to what I have mentioned.
What you might be hearing is the exhaust system cooling down. This can make numerous random ticking sounds.