My beloved 16 year old Prius is making a low pitched moan when decelerating or braking. It is not just when braking, it is whenever the car is slowing down. It also seems to be using more of its electric side rather than the gas engine. No engine lights have come on but I’m worried.
Time to get it checked out, probably by a dealer because it might be an issue with the hybrid-only mechanism. Maybe the gearbox that turns the electric motor into a generator to charge the battery while slowing has a problem.
If it is the gearbox, I’d look for one at an auto recycler.