Mine does! The engine shuts down and makes a chitter-chatter sound as it does. Sorta vibrates slightly also. Any Ideas? The car was pretty sluggish stock and I got it used.

Could it by my headers hitting something or maybe bent pushrods? There is a slight ticking sound at idle that you can hear if you listen close to the underneath of the car.

 

When you shut off the engine, do you have the clutch engaged? Mine makes a similar noise with it engaged, but not with it disengaged (both in neutral).

Headers will exacerbate the noisy valvetrain - due to different material and wall thickness. If you've missed a shift, I'd check the pushrods. If you've never checked them since buying it used, it might still be a good idea for peace of mind.