Hello,
Recently, the engine vibrate and puff sound at 1700-2000 RPM. Once I exceed the 2000 RPM, the engine run smooth.
I did some research, so far I lean toward exhaust resonator. I am not sure if I have a exhaust resonator.
Thanks in advance

 

To me, it sounds like an ignition problem.
Have you changed your timing belt recently?

If not, check your spark plugs, spark plug wires, and distributor cap.
Make sure no oil is leaking on the spark plugs.

 

Then you might also check into/read about clogged egr ports. Hard to call but at that rpm that is where clogged ports can give you "issues" close to what you are describing.