It could also be the brake pad caliper guide pins as it was in my 2013. Mine needed to be cleaned, lubed and reinstalled. Dealer Tech said they corrode due lack of use. Can you make it click by rocking the car back and forth when parked in your garage?
Had to replace rusted out rear rotors at 50k miles
I had similar but it was a consistent squeak noise. Dropped an entire $20 on replacement aftermarket brake hardware for all 4 wheels rather than just reusing old/worn parts. Brand I used had something or other 'quite-glide' using a combination of stainless steel construction, PTFE coating and vulcanized rubber that isn't found on the GM OEM hardware. Squeak has thus far not returned on my Gen1!