The hiss is most likely interference from the device, but it could also be a problem with the cd, HU, or speakers.
If the hiss only appears in your car, then its not the cd. If possible, listening to the same song on the radio would narrow it down to either HU/speaker problem or handshake.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>