iTrip and podgear sound on my car

[genesiss]

First i bought the iTrip so i could listen to music in my car, but i didn't liked it that much, because it made some noise over the tweeters, as if
they were broken, well i bought now podgear, it sounds better but still getting that sound out of my tweeters, how can i fix this??
i mean besides that everything else is great, but i bought my ipod to use it on my car. i am using itunes, and tried lowering the music volume but stiill the same thing..
should change bitrate settings, or something else??
thanks