Hello, I have a DR-40, have had it for about two years. Most of this time it has been sitting on the shelf. It has always had a hiss to it no matter what I am trying to record or what mics. Is there supposed to be a hiss? Even with the built in mics in a quiet room I get hiss. I talked to one person who said to lower the gain but I don't see where I can do that on this recorder. How can I get rid of the hiss?