I don't have any problem with bass quantity, it's OK for me, but thanks for the tip. I tried playing some bassy music with EQ cuttoff of all frequencies above 100Hz and there was no audible rattle so I think it doesn't affect sound quality much. But I worry it might become apparent with subbass focused songs and on stronger amp. When I repeat the bass shaker test from this site few times, it seems that sometimes the buzz is quieter or louder, or resonating with different frequencies (usually it's loudest at 20-50Hz, suddenly gets quiet and appears again at 60-70Hz). Maybe cables inside are touching drivers? I tried to examine it but I couldn't remove the driver even after unscrewing it, so I gave up.
That's exactly what I'm talking about when I say "control", diaphragm losing control = rattling. The HE560 diaphragm needs a good internal seal (chamber between the driver, the earpads, and your head) to pump 20-50 Hz at loud volumes without the distortion.
Try playing the tones again, but with the headphone worn on your head and adjusted correctly so both earpads are sealed well.
Could this be the cause of the "tizz", type vibration that I hear sometimes with certain vocals at a little higher volume? I hear this in the treble though....it would be my only complaint about the sound of the HE-560. and a few others mentioned this as well in the review thread. I was hoping this would go away with more burn in. Voices such as Linda Ronstadt, Loreena McKinnet, Allison Krause, as examples. male vocal Brendan Perry. Certain treble frequencies seem to resonate slightly. Can be repeated at the same point of the song!