Starter smells like plastic
First time attempting to make a sourdough starter without inoculation, and it smells like plastic, with perhaps a slight hint of gasoline. I've seen many mentions of what I would call normal fermentation odors--alcohol, bananas, vinegar, acetone--and smells that indicate spoilage (garbage, vomit), but no good match comes up when I google "sourdough plastic odor".
The only plastic the ingredients come in contact with is the container I use to weigh the flour. The flour is the tail end of a large (5 lbs?) bag of all-purpose flour I purchased a couple years ago and stayed in the paper sack it came in until I needed to refill the plastic container I keep in the kitchen for short-term use.
The smell emerged on day 3, and has intensified but not changed character through day 5. I could imagine calling it a banana smell, but that would be a stretch. It's just not quite like anything I've seen mentioned anywhere. Perhaps faintly banana-like, but also like plastic and a little like gasoline or some other solvent.
Anyone have any ideas what this could be?