Melinda,
Looks like you got good advise from everyone here.
On my car I removed the back seat. and the shelf tray at the back window.
Someone sprayed water on the rear windshield and almost immediately water was dribbling in.
So in my case, playing detective worked. I had a bad window seal. Of course my vehicle is much older.
Sometimes when you buy a car used from a dealer they shampoo the rugs seats and everything else. It may be possible that things are still wet months later and need a drying out.
Take out everything you can, floor mats, trunk mats, spare tire, look under the rugs ….Wipe everything down ….feel for wetness….to locate a leak. Break out the wet/dry shop-vac. Do all the rugs this may help getting out any moisture. Suck out any leaves pine needles ….in the drain channels under the hood etc as Peter had mentioned. You’ll have a clean car and you may find a leak !