Buring rubber smell - Only sometimes
 

98 A6 quattro.
At times I will get in my car and start it up and I get this awful burning rubber smell. It goes away after a couple of minutes. It does not do this all of the time. I am worried there is a belt or something else is not right. Any ideas?

I have found out that the smell is burning oil, and I may need to replace my valve cover gasket.