While cat is stopped at light or in park -noise that sounds like flapping of cards starts-I put it in neutral and gently rev engine to bring rpm / tac above 2. This brings the noise down. No other problems noted at this time. Sound is loud like deisel engine idling.

This is one of those where you need to play detective. Check the silly stuff first. Is it a piece of loose body trim or a loose mud flap rattling as you drive along? Is it a decorative 'stick on' accessory like a window flag flapping? Is there something stuck under the vehicle like a tree branch or a bit of trash you've driven over.
Is it a 1, 2 or 3 clicking sequence then nothing, or is it more of a constant 'machine gun' click. Start the vehicle when the engine is cold and listen for the noise. Let the engine sit at idle until it is up to working temperature, (About 10 to 15 minutes from totally cold). DON'T rev the engine! Is the noise there when it's cold or does it start when the engine has warmed up?
Does the noise happen only when driving, only while parked or both? Does it change with road speed, (faster when you press the gas and in gear, and slows when you brake), or with engine speed, (Put it in neutral and gradually press the gas pedal while you listen for any change in the noise)? Does cornering affect the sound? Use the comment button below and I'll see what extra help I can give you.

A lot cars and truck have a limiter to stop from over reving to prevent engine damage when in park or neutral. Controlled by the PCM/ECM. The engine comes back to normal idle?

James, plugged catalytic converter probable.

Have you had fuel pressure tested, as well as exhaust for possible plugged catalytic converter?

moving noise is very hard to find.

could well be exhaust shields,
did you take a rubber mallet and tap the parts (exh, end to end?)
bang ,rattle, bang , repeat
seen many bad CAT (brick inside loose) rattle. hit it. bingo. there you go.

i also jam objects in cat shelds to stop them for making noise.
just for temporary to find source.

you could have a vacum leak some where in the system that can cause high rpm,also if you have a bad tps(throttle position sensor) it can cause this type of problem.you don`t say if you have check to see what is turning on the check engine light and what code is in the computer.this should have been done and may have help to find the problem in the begining.

Sounds like maybe a motor mount may have broken,if you
open the hood and put the car in drive ,then neutral then reverse
the engine should only "rock" about an inch or so,if it really jumps
that is the problem.

sounds like powersteering pump. put it in park and open hood. have someone stand in front of engine near powersteering pump and put hand on it to feel vibration. MAKE SURE CAR IS IN PARK. Rev engine to about 2200 Rpm's and see if I am correct. Thanks and Good luck

I have experienced this. This seems to only happen when its cold out and you use the defrosters/AC. If thats the case then to fix/avoid this you can press the accelerator briefly (while in park/neutral) just to rev up the engine to about 2k or so, before you put it into gear.