Whining noise from rear of truck

My 2017 OR 4wd started making a whining noise from what sounds like the rear passenger wheel. The noise has occurred from 5-80 mph and is the same sound regardless if I’m braking or not. Toyota looked at it and said they couldn’t find any problem. After this I removed the drum on the rear passenger wheel to find the spring pin spring and cap off the pin on the brake. After putting everything back together the noise didn’t occur for a week or two, but now it’s back. I pulled the drum off again but the spring pin is intact. Has anyone had this issue? I do not believe this is the same sound others have encountered with the rear diff.

 

https://www.tacomaworld.com/threads...oise-howling-when-feathering-throttle.442341/

 

Rear diff low on fluid perhaps