Right passenger rear floor panel
 

2007 s40: rear passenger floor panel is soaked with water, I have no idea where it's coming from. My back window isnt leaking or sunroof.
please help, before I tear up the carpet to look underneath or have to pay a lot to a volvo mech lol.

did you read up on clearing out the roof channel drain tubes? Also inspect door and trunk seals, particularly if you had a recent wind-driven rain.

Mine was the heater core o-rings leaking. Very low cost fix. Very very PITA to do the actual work. My ribs hurt for days from leaning over the door sill working up above the passenger foot well.