I was doing my oil change and found this plate just resting in there. Anyone have any ideas where this would be from?

 

It’s hard to say for sure without seeing it, but a loose metal “plate” during an oil change is usually something that’s either a splash shield piece, a bracket from the undertray, or sometimes part of the engine cover or heat shield that has worked itself free over time. I’d start by checking the lower engine cover, skid plate, and any small brackets around the oil pan area first, since those are most commonly left loose or missing fasteners. If it looks more like a thin stamped steel piece with heat discoloration, it could also be from an exhaust heat shield that has dropped down.

 

Doesn't look familiar to me at all. Positive it came off your car? You could probably drive up on some ramps and poke around under the car just to make sure. It covered something so there is probably a clean looking spot where it used to reside.