Chirping from back wheel area on both sides

If the sound seems related to when the wheels are turning, safely lift and support the rear of the vehicle and turn the wheels to see if you can recreate the noise. Then, try to hone in on the cause. Areas of concern include wheel bearings and brake pad sensors (if they are getting close to worn out). Also, although there are no grooves in the rotors, make sure there is no rust build up that could be getting lodged and rubbing the rotors when moving. One other thought is the backing plate behind the rotor. Make sure nothing is stuck between the rotor and backing plate and confirm that the backing plate is not touching the rotor due to rust issues or damage.

If you are confident that the issue is related to when the vehicle is bouncing, suspect sway bar bushings or other rubber mounted component.

Rusted backing plate depends on where the rust is. If it is in the outer areas away from the inner hub just grind/sand/scrape it loose.
Bushings would depend on which ones are the issue. You might want to spray them one at a time with silicone spray and see which one(s) are the problem. Much better to know that "two lower control arm bushings are worm and need replacement" before you go in and have them tell you "Every bushing is shot and we need to rebuild the rear suspension". Also, pay close attention to the rear shocks and sway bar links, they can "sing" a bunch.