Reversing noise on 2007 Nissan Sentra

When I reverse with foot slightly on the brake, rolling down incline there is a wining/moaning noise, not really grinding but more like a moan. This is when it is a cold start. Seems like it would be back brakes, but the dealership said brakes are good. Do you have any ideas? Oh, and it is automatic

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1 answer
If your car has a manual transmission the reverse gears are straight cut and will possibly make a whirring noise when cold and in reverse.