How the heck are you getting 55k on a set of the OEM 21"??? I drive pretty conservatively and my first set lasted 25k and my second set looks to be about the same. Is your regen setting low?
Rivians run their fans automatically after the car is parked and locked to dry the HVAC system's evaporator core. They also run fans to keep cabin temps from getting too high and damaging the screen.