It's a long shot, but this is what happened to me because I'm stupid.

But basically when I put oil into my engine (my piston rings are fecked so have to top up every couple of months) I don't use a funnel or anything to route the oil safely, I basically just use the bottle it comes in and usually end up spilling it before it goes into the engine. So because of this for a a week or so, that oil is getting hot and is coming through the air vents, which causes the smell.
As I said, it's a long shot but could be the issue.