If you have a check engine light, a diagnostic code has been stored. Since your car is a 96, you can't retrieve the code without a device. Autozone can retrieve the code for free. The codes give you (and us) some insight as to the problem.
I'm not sure about the smell, possibly someone else knows. I would get the code retrieved and get back to us.
The rattling is probably a bad coupler in the supercharger head unit, but the boost appears to be fine, I don't think the supercharger is tied to the engine problem, unless it is starting to cease up.
1999 540iA Sport
Former 93 SSEi Owner
Former 89 SE Owner