Fm Mod Power

Make sure that the radio's ground is good. You may have created a ground loop with the introduction of your FM mod. Try using a RCA style ground loop noise isolator. It will break the ground loop created by your RCA cables and usually cures the alternator noise you are hearing. A power line noise filter may also be required. It is best to use the power line filter to filter all the ignition sources in the video system and connect it as close to all the components as possible. Most video product doesn't have much power supply isolation between their circuits and noise is a common problem. The two filters are usually less than $30.00.sparky