2008 Grand Caravan Loud Clicking under dash

Recently my van has started clicking loudly from under the lower dash, driver side, in the area above the gas/brake pedals. It sounds like
a screwdriver tapping agains a plastic box, 2-3 taps per second.
There seems to be a 6" plastic box of some sort there. I can't get down and look due to physical limitations.
It begins when I start the car up, and continues for 2-3 minutes then stops.
Then, when I turn the car off, it starts clicking again, and continues for a minute or so, even after the key is off, and I am out of the van.
The A/C is on all the time because of the hot dry climate where I live. A/C is blowing cold air out of the dash vents as it is supposed to.
I'll be taking it in to the dealer next week, but would like a heads up as to the problem from unbiased readers.
2008 Dodge Grand Caravan SXT
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