Here's a little experiment that might be an eye opener(ear opener?
):
Sit in your normal mix spot and open a blank session. Put up a mono aux track and bring the fader down. Insert the signal generator plugin, set to SINE and put the frequency at around 225Hz. Bring the fader up to a comfortable volume and have a pencil and paper handy. lower the frequency in small amounts and listen at each new number for a moment. At some point, certain frequencies will disappear and others will get waaaaay louder. Those dipped areas are where you likely added low EQ to boost(causing the "ugly" sound in the car). The hotter areas are where you might have done EQ cuts(which you probably didn't need to do).
