I have the same issue with my 2018 Equinox. Spare tire tub fills up with water when it rains hard. I've been wondering if my sunroof had been leaking cuz I had water in the back seat floor area as well. Could be more extensive than originally anticipated.
Not sure the reason or cause but I've noticed this came all of a sudden after I've been running my car through the automatic car wash. It's the one with the rotating flapping pads or strips. And those flaps beat on the sunroof and shark fin antenna. I may think twice about that particular type of brushless car wash once I finally get my leaking roof fixed.
