FWIW, last week I heard a noticeable but not very loud somewhat rhythmic noise coming from somewhere in my system after turning it off. It lasted for no more than a minute then went away on its own. I had been playing music fairly loud and for a good few hours before this, but the noise was neither loud enough nor lasted long enough after shutdown that I was motivated to investigate further, so I can't say whether it was only coming from my LFRs or also other speakers. However, given that the DSP is the only component that doesn't automatically power off, they are an obvious suspect.
Perhaps this is an annual Halloween Easter Egg that Ian and Andrew built into the DSP?
