Hi John,
if you are talking about the whining noise that comes from the alternator when you drive (pitch rises and lowers in time with the engine) then it is normally the fault of interference from the engine RF. This was common place in older vehicles but most newere ones have either an RF choke (looks like a lump inline in the cable) or supress it at source.

The advantage of supressing it on the cigarette lighter feed is that you do it once for everything. If you have a small iron ring (thihck one) then wrapping the power supply lead to the cigarette lighter through the ring a few times (5 or 10) normally supresses the interference enough. This is similar to the bulge you find on a lot of analogue monitor cables.

The other potential source is the power cable used to charge the device in the first place which could be just acting as an aerial for radio interference from the engine - similar idea to the first but this time around the charging cable.

Sorry about this being a UK link but should give you an idea.