Last night's experiment was to leave the heater off all night and see if it effected the odor at all. And when we woke up in the morning, there was just the mild lingering odor, instead of the awful choking cloud that greeted us the last two mornings. So, there does seem to be a connection.

The guys who installed it suggested we try running just the fan, to further isolate the cause and I'll work on that tomorrow. Thanks to all for your suggestions and anecdotes.

Finally, in a frenzy of tearing everything out of cabinets and cupboards, I realized it was strongest near the bottom of the refrigerator. I found the dead mouse in the drain pan under the refrigerator. We theorized that it was the fan from the auto defrost that made the smell better and worse.

I'll also say that skunks sometimes get spooked and will spray just enough to linger in the air, but not actually to spray onto something. I often will smell skunk spray outside my back door, where the dogs' fence is, and I think it's from a skunk venturing too close to the fence, getting barked at and spraying as it runs.