On my iPhone 6, when two sounds overlap that have different volumes, the lower of the two volume sounds plays at the louder of the two volumes. For instance, the keyboard clicks are very low, but if I'm typing when a message comes in, the keyboard clicks will play at the loud message volume until the message sound ends. It seems to be true for any overlapping sound that has different volumes. I don't remember this occurring on any of the prior iOS versions. Is this happening for everyone else too? Is there anyway to solve it? It's not a huge deal, but it "cheapens" the experience. I haven't noticed it on my iPad yet, so I don't know if it is unique to the iPhone or not.