On the engine noise problem......
Since the radio grounds through the chasis of the radio, which is probably one of the best grounds possible. I assume the factory battery ground is poor, or the amp ground is poor or just plain different than the factory. I am thinking just unhook the factory radio ground might do it, but then again, since I am rewiring, It is probably not worth diagnosing. Obviously a ground loop somewhere.
Since the radio grounds through the chasis of the radio, which is probably one of the best grounds possible. I assume the factory battery ground is poor, or the amp ground is poor or just plain different than the factory. I am thinking just unhook the factory radio ground might do it, but then again, since I am rewiring, It is probably not worth diagnosing. Obviously a ground loop somewhere.