I changed the rear brake pads only on my 2012 with 175,000 miles (side note: still on original CVT). I bled the lines and greased the pads where they contact the caliper. When I test drove it, the brakes worked fine and did not squeak. But commuting to work and back a couple days later, when I was nearing home I noticed that when I came to a stop, I heard a low-pitched groaning sound. I didn't hear it every time I hit the brakes, but only during the last couple of seconds when coming to a complete stop. The sound starts gradually and gets louder, in a descending pitch, until the car stops. It resonates like a deep bass note on a subwoofer, but not terribly loud.

The next time I drove it, I didn't hear the noise. A few days later I drove it about 50 miles and didn't hear it. But the next time I commuted home from work, I heard it, and again, only when I was getting close to home. My commute is about an hour and 15 minutes each way in heavy traffic, and is about 30 miles. I'm guessing it's related to heat, since it only happens near the end of my drive, after I've been stopping and going for a while. It hasn't happened during the morning commute, when it's fairly cool (temps in the 50s and 60s lately).

If anyone has an idea what could be causing this, I'd appreciate it very much.