That's the thing. I have trouble believing that the hiss wasn't something that was obvious prior to shipping out these first few orders. Retroactively trying to fix a fault that they were aware of but shipped anyways ain't really okay by my book, but I guess it's still conjecture on my part. However, when you sell a piece of audio equipment -- whether it be headphones or an amp, you check the noise floor as the final part of QC. Not using subjective measures like a group test, that's irrelevant (but would still catch it, really). There can't be any way that an automated process couldn't have caught the hiss.
But if they were aware of it, and they decided to ship it out anyways -- not good. I mean, if you sold me a car that you knew had faulty brakes, and then sent out a recall notice afterwards, would all be absolved?