I run a 257HP in the worst way you can possibly do it... via the 12v cigarette lighter plug in rental cars. Along with a magnet mount antenna. I think the noise blanker does a pretty darned good job. I also use the low tone setting, and that seems to help alternator whine and the like (it's still there, I just don't hear it as loud). It's a very good rig, especially for the size. I think I've had mine nearly two years now, and it is my favorite travel rig.
73,
RT307