My 2 month old Sony DA4ES now has an audible hum coming from inside the chassis. There is absolutely no hum from any of the speakers, and the unit appears to be working perfectly. I can't honestly say whether it just started, but I clearly noticed it when I turned it on tonight. I suspect it just started. The unit does not have an internal fan. It sounds like an electrically induced hum. I will try to unplug every input and output and see if it ceases. Bottom line, anybody out there have a Sony DA4ES or similar unit in the ES line that has a slightly audible hum? I need to know whether I should perhaps get it returned or serviced. Thanks in advance for any input.