I was experiencing a similar sound from the rear of my 2021 PB with 49,564 miles on it. I checked all of the obvious things off the list, removed each wheel and inspected all possible rub areas including stuck calipers, rocks in dust shields, loose heat shields, etc., etc..
Interestingly...
On vacation in Vermont for the Thanksgiving holiday with my family and my 2021 Powerboost (39,831 mostly trouble-free miles) and got the much discussed "Powertrain Malfunction/ Reduced Power" alert when we were heading out to dinner last night. Truck drove and shifted normally, including...