You need to reground your black ground cable, make sure that you strip the paint off the ground surface to the metal, then make sure you get a thick screw and a good ground loop and ground that screw in tight without stripping it, if the problem persist then buy yourself a noise filter at a best buy, car audio store and wire that in between your speakers and the connection cable.Check your battery's ground on the terminal, check to see if your radio is correctly installed, also keep in mind that if you have any cheap equipment like your radio or speakers cabling that could also cause engine noise.
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You need to reground your black ground cable, make sure that you strip the paint off the ground surface to the metal, then make sure you get a thick screw and a good ground loop and ground that screw in tight without stripping it, if the problem persist then buy yourself a noise filter at a best buy, car audio store and wire that in between your speakers and the connection cable.Check your battery's ground on the terminal, check to see if your radio is correctly installed, also keep in mind that if you have any cheap equipment like your radio or speakers cabling that could also cause engine noise.
Good luck.