It's alternator whine.
You still have a ground loop you must find.
Where are you drawing power from for the PAC?
Were/what is the ground for the PAC?
You have to ensure a good solid ground for the PAC, draw power form a clean source (ie: not on a power line that also runs an electric motor) and install it away from fans, motors, electric pumps, etc. Otherwise, it will pick up interference.
That's not the greatest line driver either.
What did you pay for it? (guessing around 30 bucks) Remember the old saying:
You get what you pay for..............