I think what you are hearing might be the cooling fan. It's possible that even when the unit is not on, and the quick start feature is on, the fan might run, to keep things cool. Because as you've noted the unit takes almost as much power off as on, with QS turned on.
I personally leave it off, since I don't like the idea of it being basically ON all the time, but I guess it's just a personal preference. Note you could try turning QS off, and see if the noise went away? It sure sounds like a fan, if you push on things and the sound changes. Especially the HDMI connector, which is mounted on the back, near the fan.
As far as the RF modulator off, if you never watch the DVDR through CH 3 or 4 on your TV, I would personally turn it off. Again it's more of a personal preference thing. I feed the RF through the DVDR to the TV and always use the TV's tuner to watch live TV, so I don't like the RF mod. coming on, and interfering with my TV reception when the DVDR is on.