My 2015 Honda Fit LX has developed a rattling sound when the car is coasting. I can briefly reproduce the sound when parked by revving the engine over 2000 rpm and then letting the rpms fall. I went under the car and the sound and vibration seems to be coming from the resonator on the exhaust pipe B. I pushed and pulled on all of the other heat shields around it and that didn't stop the noise. It only stops if I pull down on the resonator pretty hard.
What exactly is the resonator? Is there something else that could be making the vibration and making it feel like it's coming from the resonator? I pushed and pulled on a lot of heat shielding and nothing made a difference except pulling on the resonator.
Thanks!

 

The resonator is there to modify the sounds coming out of the exhaust manifold. Without the resonator, you'd hear a lot more high-pitched noises along with possibly more rattles, depending on which frequencies were affected.

As the exhaust parts heat up with continuing engine use, they expand. I'm guessing you're getting expansion somewhere between the resonator and the heat shielding, and that causes the rattle.

If you haven't done it yet, I'd go through the exhaust system and make sure there are no loose bolts that could cause the shielding to dislodge slightly and contact other parts of the system.