line drivers were invented because most of the head units only put out like 500 mV until like the 90's. It was causing a lot of stereos to be noisy no matter where they ran the RCA's. I have still have an old phoenix gold one, it had a receiver and tranmitter. The RCA's from the deck went into the tranmitter, it came out of the tranmitter at like 17 V RMS down a balanced line twisted pair cable to the receiver, then out of the receiver as RCA. NO WAY 17 V is gonna induce noise - even if you tie wrapped it to the power cable all the way down the side of the car.