Looks like snowflakes or Parmesan cheese, tbh. Not incredibly worried if it's a gusher infection (haven't had any go on me yet....*knock on wood*), no off-flavors/smells. I've regularly checked the bottles over the last month, and these things weren't there last week.
You can kind of see it here (couldn't get a good pic in-bottle):

You can kind of see it here (couldn't get a good pic in-bottle):
