Torque converter 'growl"

There is no torque converter. When do you hear the grind? When you accelerate or is it the point that the brakes are releasing and the car starts rolling? The latter may just be rusty discs.

 

I won't be as specific as suggesting rust, but this is much more likely to be a brake or driveshaft-related noise. There is no torque converter on a prius. There aren't any friction parts at all, nothing drags against anything else in the transmission. It's just gears swimming in oil like the rear diff on an old truck.

 

Maybe you have a rock or something stuck in the caliper?
Pulls the wheels and check the calipers, and the dust shields.
It happened to me and a customers car.

 

sounds like disc rust to me too. how many miles on her?

 

And I highly doubt that it has ANYTHING to do with the transmission.
What exactly makes you think it is NOT coming from the wheels, brakes or wheel bearings ?

 

It has to be torque converter, needs flushing

 

If your brake pads have moderate wear, it might be the brake module making this noise. It’s the equivalent of you pumping the brakes to bring the pedal back up. In the case of the Prius, it’s done with a pressurizing pump after the car has been sitting over night. In the morning when you oper the door, the pump will activate to pressirinze the system.

 

does it happen every time you release the brake, all day long?

 

Brake rotors. It's normal. All of my Prii have always done the same thing.

 

I wonder if something is sticking in one of the brake caliper pistons making it retract slower than normal. I'd check that by putting it up on jack stands and having someone apply the brakes. Try spinning each wheel one at a time as they release the brake pedal and see if one wheel is slow it releasing.

 

What's normal is for the Prius brake rotors to have some rust on them when you start up because they barely got touched when you parked, and there was humidity in the air. It takes a few seconds when you start out to scrub that off. If you release the brakes gradually as you start down the driveway (my typical procedure) they always make a little noise. The only fix would be stainless steel rotors (which might have some interesting results) or have the car hermetically sealed in a super dry garage when it sits overnight and never drive on wet roads, which ain't happening either. So the noise it makes when you first start out and are applying the brakes is normal. Some people put the car in neutral and stop a couple times to clean off the rotors, but there's really no need for that. It'll come off after a couple normal stops anyway.

But, as I re-read your description, it sounds a little different from what I called normal earlier in the discussion. If I had a brake piston that was sticking, I would for sure get that fixed. If that's actually what's going on. I was just expressing a theoretical cause for your car's noise. If that is the problem, it will prematurely wear the pads on that brake and, if it gets worse, reduce gas mileage and generate heat. So I'd suggest checking for that, if nothing else, to eliminate it and go on to other possibilities. Since there's no disassembly involved, it's a pretty simple check. And, if you do find a wheel that's not letting go as quickly as the others, you'll know right where to start working on it.

I hope I expressed it clearly enough. I'm kind of thinking "out loud" here.