I think burn-in makes audible change on this headphone but one aspect can be unit dependent. My first HE-560 didn't have a piano grain but this second one did. After burn-in, no piano grain and the bass developed.
That's not why I'm writing today though. Something worse happened than grain this weekend...Sub-bass rattle in the left driver. Thought it was harmonic distortion at first because it didn't sound like how my first HE-560 rattled but then I realized it was the driver making the noise, once again. Back to square one and I'm not sending this one back. It was straight from their supply store, so recently made I'm guessing. It's mainly noticeable on quiet sub-bass, so A LOT of the time. I wasn't aware of this issue from the reviews so I added a note in mine as well as how to fix it.
According to jerg, sealing the pads to the driver from his mod fixes it . My amazon order for the glue is going to take longer than expected so I'm gonna have to go to the local store if I wanna get it fixed this week. Minus half a star from my review until it's fixed. I'm being generous because the sound unhampered really is incredible at this price. And not to doubt jerg but If it doesn't....I'm gonna get mad a. A problem like this shouldn't exist at this price point, in high end products. Shouldn't exist even for lo-fi.
So, all in all, if it works for me then jerg's mod has an objective benefit for the HE-560 irrelevant of sound preference. Thus blind comparisons won't matter for this.
This better not have potential to happen to the HE-1000 too, or Hifiman has problems. If you have to mod those to fix something that has nothing to do with subjective tonal balance then it's a huge issue. People better let Hifiman know if it happens to the HE-1000 beta unit. I would have let them know if I was in a HE-560 beta, took me less than a month to notice both times. I heard they had their driver design issues but didn't think something like this could happen with the HE-560. What makes it even worse is this is a unit that replaced one where the same happened so it's a HE-560 issue like jerg explains.
Hope this helps other people as I don't think many are aware of this.