iPhone 4S hissingstatic when plugged in AuxAux in Car

Does anyone have a good fix for the 4S hiss/whine when plugged into the aux port in the car?  I just got the 4S, plugged it into the auxilary port in my car, and there is a high-pitch hissing/whining.  My previous iphones, same car, same cable, did not have this problem.  We plugged another 4S into the port, same problem.  I bought a new high-quality cable and the static is gone but the high-pitch hiss/whine still remains when any audio (phone, itunes, etc) is played.  The noise stops after the audio feed has stopped.  From what I see online, this is a known issue and it is occuring more frequently with BMW's (??).  I've heard that the ground loop filters sometimes work and sometimes don't.  It seems like the aux to dock connector output might be a solution, but I'm wondering if anyone has tried it.  I'm looking for a solid fix (not just turning down volume on the device)...does anyone have any input?  Thanks a bunch!