1994 Toyota Camry

Does the car have 24,500 or 245,000 miles on it? Is it comming from inside the engine? Make sure all the drive pulleys are in place. If the later milage is true then has the engine been rebuilt? What kind of oil pressure do you have?

The milage is actually 245 000 and the noise is around the engine, near the belts I guess. And I dont think the engine was rebuilt. There is a "engine check" warning sign coming up on display along with "O/D off" sign flashing as well. According to the manual, there maybe a problem with transmission.

"O/D off" is overdrive off. There should be a button to activate it. If it does not work then most likely there is an issue with the switch or solenoid on the transmission to actuate it into overdrive.

You need to check the oil pressure immediatly if you have not ever rebuilt the engine. The rattling could indicate extremely worn rod bearings (excessive play in the piston rod), piston slap (form excessively worn piston rings) or a worn main bearing. Does it burn oil excessively? If not then you could probably rule piston slap out. Even the valvtrain could have problems, such as a sticky lifter or extremely worn spring. The key right now is to note oil pressure.