Over the last few weeks my 2010 Subaru Impreza (sedan, 2.5L non-turbo with 4-speed automatic transmission, 154,000 miles) has developed a metallic rattling noise in the rear right-side of the car. The rattle only happens when the car is at a standstill and the brake is pushed in. As soon as I lift my foot off the break and start going even just 1-2mph, the sound goes away. And when I slowdown for a red light the sound doesn't appear until right when I come to a full stop with the brake pedal pushed in. It also only appears to happen when the car is in Drive. When I shift to Neutral or Park it goes away, but then comes back as soon as I shift to Drive. The cat was replaced about 40,000 miles ago by a previous owner, and I thought that could be going bad, but there's no rattle when we're accelerating or decelerating. I also figured if there was a loose heat shield or exhaust fastener it would keep rattling while moving and not just at a stop. I just had brake pads and rotors on all four wheels changed, could it be something came loose or wasn't properly reassembled during that? An issue with the Brake Fluid? (The Brake Fluid level is at the max, but I'm not sure when it was changed last.) I did find a small rat nest under the trunk liner panel (we live in New York and park the car on the street), but didn't see anything loose back there otherwise. Any advice or insight would be appreciated, thanks!