Why does your 1996 Nissan pickup rattle when idling and slowing down but stop when clutch is engaged?

If the noise goes away when the clutch pedal is pressed down, then the problem is most likely the clutch throw out bearing.

It may be the stainless steel shrouds on the exaust pipe. My 1994 truck will rattle when the engine is at a certain speed. The screws holding the metal together have begun to rust out, and the loose pieces are making the rattle. My 1994 truck does just the same. About 3 years ago I was advised by the dealer to replace the timing chain immediately for about 1600.-$CDN (typical advice for a female...) and shrugged it off ever since. I just replace the engine oil more often. I read a few times that the models around 1994 have a slightly lose timing chain causing the intermittent rattle but are of no major concern. I will post again if my engine blows up after all....