I have had no issues with "hissing". I'm hearing mild crackling on a very regular basis. It's easiest to hear in the menus, where things are quieter. I've also noticed during intense gaming the sound will occasionally clip out, for a split second.
Yes, I've attempted to update the controller again, with the adapter attached. As I said earlier, both of my controllers exhibit the exact same issue, and the actual headset gives me no crackling when plugged into other devices, like my phone. It's clearly an issue with the adapter itself, or the software OS processing it all.
This is one of those things where I'm beginning to wonder if everyone has some mild crackling, but just doesn't notice it.