It isn't another object in the car causing it, I've already tried removing everything from inside the vehicle. I also checked the visors, adjusted the passenger seat in multiple positions thinking it might be the seat itself, etc. It is definitely coming from the front passenger door panel/window. I tend to hear it near the pillar area but not always.
I will check this and let you know what I find. I don't remember the window being loose but will check it again.
I had one of the service techs do a ride-along with me but of course it didn't make the noise then. Its also been very cold lately and it tends to do it more frequently the higher the outdoor temperature, which may explain why I started noticing it toward the end of last summer.