My Benchmark DAC2 USB would on occasion do the same. I figured it was receiving an input signal from something that left it triggered on. I now have the newer DAC2 HGC there is always one light on & one light flashing. I only just hooked up the HGC and have not had time to mess with it at all other than a short listening session. I am hoping I can get the lights to go off.
-John
-John