I noticed increasing rattling/roaring from the engine which -interestingly- was a bit worse when the engine was warm. Taking a close look and touching here and there under the hood, I found that grabbing the air cleaner body made the rattling disappear. It was caused by the air intake duct hitting a wire wrap (from which nothing good could come in the long run) and 3 loose fittings in the air cleaner body that allowed it to shake like a maracca:
With the resonator out, you can see that the shaking problem was mitigated in the assembly line by sticking some padding to the air intake duct connection, but the normal engine vibration has worn it down (38K miles), as well as the plastic in the air intake, resonator duct and their corresponding fittings in the air cleaner body. The wear is deeper than what it seems in the photos:
My admittedly crappy fix was to add a few layers of electrical tape around the loose joints: