240SX - Rattling noise - What to do ?

It could be a number of things, some more expensive than others:

- Something may have come loose. Check around the engine compartment (engine off) for anything that rattles when you move it.

- Gas is too low octane & the knock sensor has died or can't handle it. Nisson recommends premium for this car.

- Loose or damaged heat shields on the exhaust pipe.

- Ribbed fan belts make a rattling noise when they get old and start cracking. My '91 did this. It sounded exactly like timing chain rattle.

- The radiator fan clutch could be on the way out.

- A failing motor mount can allow the engine & transmission to move when accelerating. This can cause all sorts of weird noises, a rattle is one possibility.

- Bearings in belt pulleys can also make a rattling noise in the early stages of failure (prior to the banshee-like scream and then flying off).

- The timing chain guides or tensioners could be failing. That tends to be a rattle in a specific narrow range of RPM, likely around 2000 RPM. Try holding the accelerator steady at different RPMs in neutral and see if it will rattle for you.

There are more. This is all I could think of just now. If you can make it rattle while in neutral, open the hood and get somebody to watch and listen. If its not bad gas, you should be able to isolate it, maybe with the help of a makeshift stethoscope (piece of hose). Be careful not to get caught in the spinning parts.

Does it come from Below the Car?? If so, it is the Heat deflector. If in the engine compartment, it is the Timing chains... Change them ASAP