As long as you just use the iPod on battery power, it sounds great. Once you use the H/K or any other 12v supply to the iPod, you will undoubtedly have a ground loop issue (hum/alternator whine). There's another thread on this forum complaining about this issue. The H/K provides some isolation as the hum/whine was noticeably reduced compared to using the Apple 12V adapter, but it was still annoying for me. Other have found it acceptable. So I ordered the Crutchfield ground loop isolator and tried that. When I used it with the H/K audio output, the frequency response was drastically reduced (sounded like an AM radio), but plugging the isolator directly into the iPod output (and using the H/K just for control/power) works great. The sound is amazing. I think there is an impedance mismatch between the H/K and the isolator. The H/K probably wants to drive a line level input and the input to the isolator is probably optimized for the headphone output. I've been toying with the idea of trying another isolator that is meant for line levels, but just haven't gotten around to it yet.