I have a 2003 Corolla which was shaking pretty badly upon braking. I replaced the front rotors and brake pads—and everything went well. After a couple of days of driving, I began to hear a harsh grinding noise; it sounds like a low, raspy metal on metal grind. At first I thought it was coming from my passenger-side brakes, but after checking and re-checking brakes on both sides, and paying more attention to where the sound is coming from, it actually sounds like it's coming from the rear passenger side.
The sound gets worse the slower I'm going (so, if I brake at 60mph I can barely hear it, but when the car is slowing down to ~30mph, it's very pronounced). It also persists for a little after braking, when I begin to accelerate again, but generally I don't hear it while not braking.
The rear brakes are drum brakes. What might be causing this? Is there any reason why changing the front brakes might affect the back brakes?