Just popping in here again with a somewhat bizarre story with my DT880. Earlier today, while investigating some rattling that sounded like it was coming from inside the right cup, I took off the pad in order to pry off the baffle. And under the pad lip I discovered several casings from (former) insect larvae.
That's right.
There were things living in my headphone! Both sides, too, as it turns out. Checking inside both cups, I (thankfully) didn't find anything. The rattling seems to have been coming from the adjuster mechanism on the right side, which is getting a bit loose. It's not an issue once the headphone is properly seated on my head for a while, and it certainly doesn't affect the sound.
But, you know,
yuck. I have no idea how long those things were in there, but it's highly likely I was actually using the headphone while the larvae themselves were still present. After this disturbing discovery I decided to give my pads their annual soapy water bath several months early this year. Now they're clean, dry, and hopefully insect-free.
Moral of the story: Clean your pads periodically. Or, at least, check under them from time to time. You just might find some unwanted guests.
Also, now I know how this guy must have felt:
http://www.head-fi.org/t/609792/ants-in-my-stax-should-i-worry