[svx_commuter]

If that is the smell I think it is then it was more common on the new 97 OBS I had. It is the black rust proofing coating that is sprayed all over the bottom of the SVX and other Subarus. I have noticed that when the tranny rear seal was leaking it softened up the coating back in the tunnel area. Now it is completely gone from the spray area. This just proves that it is petro based and oil soluble. In your case it may be that the under coating is melting in the area of the pipes between the engine headers and the first cat. Those pipes get pretty close to the bottom of the car and all the engine heat channels out through that area. After it melts it would release the odor.