I've returned 3 units to the store today, and now I'm looking at taking back the 4th one as well. The home button on the first three was not flush with the surface, and now the 4th one has a distinctly lower maximum sound volume than my iPad 2. Has anyone noticed a sound problem with this new iPad? I'm playing back music, videos etc., and those whom I've demonstrated this to all agree that the sound on the iPad 2 is louder and more robust. I first noticed it with the keyboard clicks, which were definitely of lower volume than the iPad 2. And yes, I have both units at maximum volume. Thoughts? Thanks.