I presume this is when its plugged into some amplifier with a high input impedance?
Fixing this might be tricky as the output caps on the Audio Adaptor don't like a low-impedance load (it compromizes
bass frequency response), yet adding lowish value load resistors (~1k) to the line outputs would reduce the noise
when powered down (which otherwise makes the outputs very high impedance and thus allows the power amp to
see its own bias resistors' Johnson noise).
This is a problem common to many portable music players these days when plugged into a power amp (its poor
audio design, its not an uncommon use-case)
