[RICK LAKE]

As others have said, all mounting points going to the frame need to be greased. Pull apart 1 mount at a time to no effect alignment of front or rearend. Grease bushings and bolts and both surfaces and reassembly. Do this to each mount. put car back on ground and tighten bolt and nut to spec. This will stop binding of joint. Start in front end and work your way around the car, 1 corner at a time. Shock mounts too. Don't over tighten nuts either. This will causing binding too. The noise is suspension if going over bumps. Rattles will be body noises or exhaust. Chassic ears will help track down location. Last side note, you brought a cobra, It's loud, noisy, clunky, nasty, and abusive. You could spend the next year removing noises the car makes with foam, insolator backing material, and other noise reducer tricks.
My other thought is the suspension springs are to high for what you where looking for. Maybe drop the spring rate 100 pounds and roadtest the car. If the shocks are adjustable on compression lower the setting. You will lose car handling and may help for a softer ride. Rick L.