'06xc70 pass heater blend door oscillating from open to close

[whichcraft]

the passenger side climate control blend door on my '06 xc70 oscillates back and forth from "open to close" all on its own whenever the system is in use. the car has 160K, was purchased used, by me, from a small used car dealer/butcher in 2021 with 81k on it. I have removed the kick panels to observe the activity/look for any obvious issues, have vacuumed out the CC intake port on the console...nothing obvious. The system does blow hot and cold air w/regard to A/C, heat etc. when in use and the drivers side functions correctly. Makes being a passenger in my car.......not so nice on most days.