Almost a year after purchase, but it was moderately used at best. More kinda like a backup hp, as I do most of my listening with my stax rig.
But definetely more that 120hs, as my burn-in alone was something like 300-400h (though with low volume level).
On the other hand I cannot surely say when the problem occured.I've noticed it lately, but it is possible that it had been this way since a couple of months, because at first I haven't really paid attention to rattle: I was thinking that this may be caused simply by my bass eq. But then I've realized that this should not be the case, as bass lines in opening of Dragonborn go low, but the volume is also low, and I have permanent Foobar gain setting at -5dB. Thats when I began investigating the problem and realized that this has to be some kind of damage to the driver.
I am waiting for my D7200 to be back with me, as I bought another set of 009 pads as per Zolkis recommendation. I already have Dekoni lambskin ones so I will try to compare all three sets here.