It seems that when I play my iPod thru my DLO Trandpod Direct (NON FM MODEL) Charging Cradle I get a high pitched whine in time with the engine speed. Especially wheh the AC on!

After further trouble shooting it has been narrowed down to just happening when the Transpod is plugged into the lower Power Outlet on the console. When playing the iPod on it's own battery, or when the Transpod's plugged into the Upper Power Outlet the whine goes away!
My local Stereo Shop diagnosed it as a "weak ground" which leads me to my question. Where are these Power Outlet grounds located?
Any Help will be greatly appreciated.