Rear suspension noise over very small bumps only

Had new (but cheap) shocks replaced in May along with rear rotors and pads. At that time, tech noticed one of the rear coil springs was broken. Replaced both rear springs in June. Now, when driving slow (less than 15 mph), and going over very small bumps, there is noticeable rear rattle. No noise when faster, going over large bumps or on the highway. Tech just replaced rear sway bar bushings, as he said there was some play there. No change in the noise. I am wondering is installing new and better shocks the answer now? Also, possible replace mounting plates as well.