We've just bought a 2003 Nissan Pulsar N16 Sedan, and have just begun to notice a knocking or dull rattling sound from underneath - but mainly at low speed over minor road bumps. Otherwise the engine, gearbox and ride are very smooth (and almost 'as new' feeling).

We had similar symptons with our last car, which turned out to be drive shaft - so are hoping to rule this out!