I have come to believe the problem is really when the volume is cranked up.. since the car is somewhat loud ( lets not start that discussion again!) and when you push up the volume the treble becomes harsh..

The treble is probably harsh because Bose's frequency ranges are out of wack and not on normal levels...

Is this something they can fix?

No, its how their speakers are made. I know a bit about it because of home theater systems and Bose refuses to release their spec's for their speakers.