Loud, metal-scraping noise & foul exhaust smell when start

couple known issues:

there is a cold start knock sometimes, if you previously shut the engine down before it had fully warmed up, like moving it around the yard and shutting down immediately

the egr circuit probably needs to be cleaned. do this before the head gasket blows
this problem tends to show itself around 100,000 miles

 

Stupid question but anyway: you've checked the oil on the dipstick?

If it was severely low there'd be a warning about oil pressure (red, looks like a genie's lamp?), but who knows.

Also, who did the oil change?

 

If it is "rotten egg" smell, it could be your catalytic converter. This is designed to convert hydrogen sulfide in your engine's exhaust into sulfur dioxide. The rotten egg smell could signal that your “cat” isn't working as it should. This does not explain the other part of your post.