Head unit noise

 I have a 95 lexus es 300 with a new sony head unit. Problem is with the switch on(Not running or accesory position, just on) the stereo is fine no noise or anything. As soon as i turn it to accessory , You can hear a low hum. And when the car is on there is the old alternator whine. I had purchased a 20 amp noise filter for the power to the head unit and that had no effect. I have run a direct ground line to the unit itself and still the noise remains. I even have 2 ground loop isolators for the rca inputs, so all signals leaving the unit are filtered. no good. Have checked rca's for cuts , no power wires/speaker wires together. ANY help would be mucho appreciated!

The amp for the front is mounted under the seat directly bolted to the body, where the passenger seat is. I have removed the amp from the setup(completely ungrounded w/no power), and still have the same noise with the head unit only. But no noise with the car switched on, just with the acc and running. I also have added new battery terminals today,gold connects. I have read that installing a second main ground to the body from battery can fix this(?). Not sure though.