I've noticed my tweeters seem to sound harsh when I get up to highway speeds. I have Focal IS130s (5 1/4" , mid + tweeter w/ built in cross over.) Because the crossover is built in, there's really no way change the crossover point on the components I don't think. The tweeters are mounted at about chest level on the door, opposite of the side mirror on the interior.
The only way I combat the harshness is by turning the bass up on EQ and turning the treble down. It helps, but I lose the quality of cymbal hits and risk clipping by messing with bass settings.
What's causing this and is there any solution? Perhaps Dynamat?