04 w/ Bose system...I have a Metra kti and this headunit:

https://www.amazon.com/MODEL-PIONEER...r+avh-p1400dvd

Like several others that have installed an aftermarket headunit, I am getting an alternator whistle.. I've trying grounding the headunit several different way but it always shows up... Am I missing something? Is it more than grounding properly? Where's the ideal place to ground? Do you guys use the ground wire or just attach to a metal piece of the head unit?