Four years late to the party, but I had the exact same issue that happened to be getting gradually worse. Took the left earpiece completely apart, looked for bad solder joints, dust, etc., but didn’t see anything wrong, and put it back together. I haven’t heard a single static sound or crackle ever since. My best guess is there was/is a bad wire and when I reassembled it, that relieved the strain. It’s been about a year and they’re still good.