hmm, funny you should mention this. i was just noticing this morning that i have a very faint alternator whine when using the tuner. it took me four months to notice it, so it obviously isn't very bad (then again, i don't drive that much, and i use the tuner only occasionally for NPR).

in my case (a 2000 isuzu trooper), the antenna is amplified, with the power supplied by the factory head unit. frankly, i'm surprised i don't have a ton of ground loop noise, but the mp3 playback is as noiseless as can be.

--dan.