The noise you are hearing is due to the DCDC converter switching from 12.x mode to 14.x mode. Specifically, it's an inductor that squeals when the ECM changes between modes. It won't damage anything, but if you'd like to make it go away - and keep your 12 volt battery more charged - you can cut the WHT/GRN wire going to the DCDC, which will force the DCDC to charge the 12 volt battery, even when the ECM thinks it's not mpg efficient to do so. All you have to do is cut that wire and nothing else. I've been running my car this way for a couple years now and love that the 12 volt battery is always charged. FYI: There's only one WHT/GRN wire in the IMA bay.