Burnt smell in cabin at high speed in cold weather

[JBinc]

I have a similar symptoms with my '07 Yaris 4dr w/205K miles. I was driving on the highway and suddenly my exhaust was twice as loud as normal. I put it on a hoist yesterday and found that the connection point where the pipe from the exhaust headers meets the section of pipe just before the cat was loose. There was no spring between the two flanges, just two bolts. I'm thinking the gasket deteriorated, causing the gap resulting in the exhaust noise.

This connection point in the exhaust lies just to the right of the driver's foot on the underside of the car. It's possible the exhaust gases from the leak are heating things it wouldn't normally come into contact with. Maybe your heat shield is also gone (due to rust/deterioration). Check this point in your exhaust if you're able to get under it.