Bad oil-Exhaust leak

Hi, yesterday I put two quarts of oil in my car (it was down two quarts). When I went to open the second bottle of oil, I saw that it had already been opened. This gave me some pause, but I did not think anything bad could happen, so I poured the second bottle into the engine. The contents looked exactly like the contents of the first bottle, same color, same consistency.

When I started my car, the engine was much louder and it made a loud "purring" noise - not in a good way. It sounded a bit like the muffler might be starting to come off. That seems like quite a coincidence, that this should happen right after putting the (maybe) questionable oil into the engine?

Today the noise is even louder and it also smells like exhaust inside the car. I was only in the car for about fifteen minutes, and had all the windows open, but I now have a bad headache.

What could have been in that oil to cause this, assuming that the two things are even related? Has anyone ever heard of something like this happening? I know food and medicine gets tampered with sometimes, but motor oil?

I know this is a weird question, but please, only serious answers. Thanks.