Plase help me identify this rattle.

[c.f.169]

I posted this in the small questions thread with no reply.

Originally Posted by c.f.169

Please help identifying this rattle. The rattle is very prominent in the exhaust area. Not from the front of the engine. This only happens on cold starts and only lasts for a fraction of a second. If I turn the car off after the first initial start and start it up again the rattle disappears. Does this sound like an exhaust leak. Thanks guys.
*EDIT* This noise started after I did my rear main seal. I had to remove the down pipe/ exhaust to remove the transmission. The Exhaust manifold bolts are all tight, as well as turbo to manifold. I'm stumped, but its definitely the exhaust side. The heat shields are removed to eliminate the possibilities.

I changed the ehaust manifold gasket and the noise is still present. Anyone? Does this sound more like wastegate chatter, or a sticky valve or exhaust leak?
Here is another video from today.

Hopefully I can figure out what this is. Thanks in advance!