Thanks folk, we have had a wet spell this week, which may have contributed. I have been keeping it under a covered porch.
The odor is like wet smoked wood, not real stanky, but not a "clean smoke" smell either. I do believe the culprit may be some grease that got somewhere I missed. It is surely not the grates - they are sparkling . I'll check it out tommorrow, and probably (reluctantly) clean and re-season it.