Here's a guess -
Often Toyotas of that vintage would have the sunroof drains that exited via the rocker panels. The drains slots in the panels would become clogged and water would accumulate inside the rocker panels.
Perhaps you're hearing ice chunks (you're in CT, right?) and water sloshing around in your passenger side rocker panel.
Best way to tell is to look under your rocker panels and make sure the drainage slots are clear. There are subtle little slots that you can clear with the end of a zip tie. These should be located along the pinch weld seam. Also, there are probably plastic plugs you can pull out.
Good luck!