How do I stop noise in my car stereo system?

In the 1990's, Dolby S noise reduction was introduced to the compact cassette, derived from Dolby SR, a professional system. Whereas the Dolby B and C Noise Reduction would dynamically adjust the preemphasis to promote a lower noise floor for high frequencies, Dolby S worked across the frequency range. However, licensing restrictions meant that Dolby S was only available on higher end tape decks that included dual motors, triple heads and other refinements. This system, according to a double blind study conducted by Stereo Review, yielded more accurate results than MiniDisc.