Water sloshing behind dashboard

Hello,
Reading different forums to figure out how to solve my problem. There is water sloshing
around behind dashboard that can be heard when I make sharp turns. This just started
about one month ago. Faint at first, but now sounds loud and clear.

A few places I've read say that it could be low coolant levels. If my overflow tank has
coolant in it, then low coolant would not be the issue? Correct?

Next, I've read that the AC drain may be clogged. I have located that in the engine
compartment and will attempt to clear with some stiff wire or pipe cleaners. If that does
not work, what would the next step be.

I have also read that drains in the tray below windshield wipers may be clogged. How
do I access these drains without taking the windshield wipers off?

I am also wondering about the seal right underneath the windshield wipers, what that
should look like with the hood up. It is curled, for lack of proper description, on both
sides then straightens "up" in the middle of the car. I see photos can be posed, which I
can do tomorrow.

Thanks ahead for any input. I am getting worried the water may freeze and cause
damage.