No water anywhere in the back, but it has been a few days since the rain. There are some minor signs of corrosion. I noticed that the right vent port on the battery is not plugged like it should be, so some corrosion might be due to hydrogen gas. Wire harness grommets look OK at first glance.

I'll soak it down tonight, and take some before and after pictures.

If it turns out not to be water in the back, are there any control modules under the hood that I should check? I recently replaced several plastic partitions in the engine compartment so that the long weather strip at the back of the engine would seal to the hood properly.