My friend has a 2007 Subaru Outback (with an NA EJ25 motor, 140k miles, automatic) that is making a noise when he eases off the accelerator pedal. It seems to happen when the engine hits over 3k RPM and then releases the pedal. The noise happens when he's both driving and parked. But at idle, the engine sounds just fine. The sound seems to come from the underside of the engine, near the exhaust, but I can't pinpoint it too well.
I've checked the heat shields around the cat and exhaust manifold and none of them are loose. I gave everything a good shake and it all feels solid. There is minimal to almost no rust around the exhaust too.
Here is a video of the noise: https://youtu.be/Yd8Qwt7Gqzc