Had a similar problem with my '22 ST. I think I have tracked it down to the rubber relief bladder mounted behind the driver side wheel well lining, on the engine side of the firewall, below the engine bay fuse box. On the liner, removed a pop pin, a small retaining screw, a nut-washer in order to deform and lift up the cloth-like lining to expose the small rubber bladder. Pulled bladder out and cleaned out LEAVES and popped it back in. I imagine that under heavy rain conditions the blocked bladder was unable to service the volume. I also ran a weedwacker nylon line down the drain line from the front driver side corner of the sunroof channel. Tested, clean flow now.
TWO notes. 1) I'm going to check out passenger side soon as I imagine that might be a future problem.
2) In both corners of the window cowl/wiper area, both drain to the outer edge where there is a gap that leaves can also accumulate and fall into the drain area with the bladder. Bad design!