Here's a simple way to improve your car audio quality: sound-deadening materials. In most cars, the speakers are mounted in the front doors and behind the rear seats, usually facing up towards the rear window. The vibrations from these speakers can actually shake the car (or parts of the car), which can be noisy and will generally reduce the quality of the sound. Sound deadening materials like Dynamat and Hushmat can absorb these vibrations when properly installed.
Click the images below to view products by Dynamat and Hushmat.