2016 Nissan Altima - we bought it in June. It is high mileage, 60k.
Last few days leaving work I’ve heard a low metal noise from the back right tire, it’s there driving but worse braking. The sound goes away when you come to a full stop and start driving again, or sometimes just randomly after a few seconds of driving.
Sound like new brakes? I’m a car idiot - I will be taking it to the shop just wondering what to expect.
Thanks for any guesses 
Yup probably
Your brake pads contain a bit of metal that is exposed when the pads are worn-down almost to the point of having no pad left, and that bit of metal serves as an auditory warning that you need brakes–imminently .
So, as soon as you hear that noise, it behooves you to take the car a.s.a.p. to a mechanic.
A competent mechanic will check the condition of the brake pads on all 4 wheels, so don’t be too surprised if you need to have brake work done, all around.
When you have your brake pads replaced, that is an excellent time to have the brake fluid flushed/replaced also. Even if the Nissan maintenance schedule doesn’t list this procedure, it is important to flush/replace your brake fluid every 3 years.
The brake pads have wear indicators. These are metal tabs on the brake pads that come in contact with rotors when the brake pads wear to a certain point. This can cause a metal-on-metal sound when the vehicle is moving and when braking.
It’s the shinny thing on the back of the brake pad.
https://www.rockauto.com/en/moreinfo.php?pk=7474388&cc=3353625&jsn=418
So, the car probably needs a rear brake job.
Tester