I have a rattle when the car is at 2000 RPMs while

You need to check the engine for a vacuum leak, use a spray can of carb spray and lightly spray around engine (do not get on paint finish) when you hit a leak the engine idle will change

My Jeep Grand Cheroke Limited 2000 did the same thing and the dealer replaced the O2 sensor and problem was solved. It about drove me crazy until it was figured out.

Thinking there is a rev limiter on that car,designed to work only in park and neutral
Sounds like maybe it's staying on,
My first thought would be the neutral saftey switch on the ******.

Check the tachometer while changing from from neutral to drive; you should see a change in the RPMs. Rattles have a resonant frequency and the minor change in engine speed may be causing it to reach resonance, making the rattle more apparent.

Hi Tom your vehicle is equipped with a Rev limiter it will not allow you to rev the engine above 4000 with the trans in park; as for the first problem you may have one of two things, one of the spark plugs or spark plug wires is bad or you have a flat spot on the throttle positioning sensor in which case have be replaced. Good luck?

throttle positioning sensor

your exhaust pipe is rattleing near or at the convertor

hav u done your needed maintenance like checking oil level-itz done with engine going in park also shift cable needs ajusting or solenoids on the electronic models if alot of miles then a rebilt is posible am tired and its late-try testing the tps sensor 1st has to with shifting***

I had the exact same problem on my 04 GC. I put some Techron Concentrate Plus Fuel System Cleaner in from Wal-Mart and it seemed to fix the problems right away. Let me know.

Sounds like a fuel pressure regulator is bad