EPS is relatively new, and I’m not sure automakers pay much attention to AM radio anymore. Whine comes in either through power (needs filtering) or via the antenna, which means the source needs some kind of shielding or other trick. You could experiment by installing a power conditioner in front of the radio and/or perhaps adding supplemental grounds between the rack, the battery and the alternator. i would not enhance grounding between the rack and the chassis on the first attempt, I’d play with that after the others first.