2016 Toyota 4Runner, 90K, 4WD, automatic, no codes, no apparent damage, no off road, no towing, no unusual use of the car. Every season for the last 4 years when it is cold, less than 55F, a faint grinding/rubbing sound shows up which can be heard and gently felt through the floor board when driving. Seems most obvious when going 15-50 mph. It is periodic in nature, about once a second when driving slow, frequency increases with speed. When the car is driven for few minutes, dare I say warms up, it goes away. It also goes away when put in 4WD (simple part time 4wd). Differentials, transfer case, transmission fluids changed, all looked normal without bits and pieces coming out. Wheels spin freely, brakes have been replaced a few times over years with no effect. Drive shaft greased. I do all my maintenance myself with care and your youtube guidance. I'd roll my eyes at that too but any idea what it might be? Thank you.
Blazej
Your front differential even in 2WD with the hubs not locked is gonna spin just from centrifugal force of the gear oil being moved. Especially when cold because it’s thicker then. And since the driveshaft will spin a little to you are probably hearing the yoke spin freely in the transfer case. When it warms up and the gear oil thins out it’s more likely to spin a lot less or not at all. This would make sense as you say it goes away when you put it into 4WD.
