I've had my MB800 for about 5 months, no hiss or whine problems and it's been a great amp in my experience. As was already stated though, I would buy from somewhere that has a good return policy and I would also register the warranty immediately if you do buy one. Between those two things there's no reason even getting a "bad one" should be a major issue, as long as you deal with it promptly through the proper channels, since you should be able to have it exchanged or repaired with minimal hassle.
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