About 2 months ago I started having the exact same problem with my first-gen 950 (one of only a handful that didn't have the hiss problem). Happened on all digital inputs. The only pattern I could establish was that it would happen after the system was on for 6 hours or so (a common occurance in my household). Went through the same series of tests, plus Steve had me get power from a different circuit and get the 950 out of the equipment stack to rule out heat issues. Nothing changed, so my 950 is currently at Outlaw getting the once-over...