Hey 08micsta, have you tried altering the equalisation settings on your iPod itself?
Not ideal, I know, having to keep juggling settings when changing between car and headphones, but when I had a fiddle with mine (no carry on-esque comments please) I found that I could get the rear view mirror rattling with ease.
Try moving to a more bass-heavy equalisation setting in your iPod and you should be ok.....