I agree with hellokit. If you use synthetic oil, it smells to me more like burning plastic than burning oil when it leaks through the valve cover gasket and gets on the exhaust manifold. Also, though others will disagree, I seem to have more trouble keeping synthetic oil inside the valve covers on my BMWs and Volvo. I have replaced several gaskets and still have problems with that.
The second most likely culprit is an overheating catalytic converter due to engine misfire. The catalytic converter may be cooking the undercoating, carpet padding, or carpet. That is only a problem when you are stopped. When you drive, air moves between the ‘cat’ and the car so you should be OK to drive it to a shop.