hey guys.. anyone tried hooking up their iphone 4 to their car with an AUX cable through the headphone jack?

i'm getting horrible sound.. very faint.. i have to crank the speakers all the way up but hear the buzzing noise. i've checked my connections and they're good.. i've used the same setup and cable with my iphone 3g and it works well!

any ideas/advice?!

thanks..!