two possibilities; a power problem as you've already pointed at (and that can be tested), the other would be a chip failure. My first unit had a chip in the adc/dac/clock areas start to fail and it started like what you're describing before slowly gaining steam. SD took care of that and swapped units (I was still in the first year with that). If I were you, I'd test the power first and then talk to SD about it if connecting to a wall outlet or phone charger with a different cable doesn't point to your power cable.