Volvo Repair: Volvo 240 1989 smell problem, rear defogger, 1989 volvo 240

Question
I have a 1989 Volvo 240 sedan, and for some reason, every time I turn on the back window de-fogger (sorry, I don't know any technical terms for cars) the whole car fills with a digusting stench that literally smells like dead, rotting fish. I cannot figure it out. I cleaned to metal strips that heat the window just in case something had died on them and when heated they gave off the smell, but it didn't work. Maybe the glue or adhesive that was used to keep the metal on the window has started to come off, and the heat makes it smell? I have no idea what to do. I don't ever use the de-fogger anymore because of the smell. Any ideas? Thanks so much.

Answer
Betty, I can honestly say that this is a first for a rear defogger.  If you were talking heater then I would say an evaporator.  This is something that I have never seen or heard of.  You may want to ask one of the other experts if they have seen this.  Good luck.   Roger