Grinding noise from rear brakes — how urgent is this?

Grinding means pads are gone and you are metal on metal, rotor against the backing plate. Every mile you drive is scoring grooves into the rotors, which means what could be a 40 dollar pad job is turning into a 150+ pad and rotor job. More importantly, your stopping distance is significantly increased right now. This is a safety issue. Get it done ASAP.

Rear brakes on a CR-V are one of the easiest DIY jobs. Harbor Freight brake pad set: 20 bucks. YouTube video for your exact car: free. Basic socket set and a C-clamp to push back the piston. You can do this in a parking lot in 30 minutes per side.