ya... hu is grounded to the back batteries, RCAs are grounded to the HU case. neither did very much good.
everyone always says "check the grounds" for every problem. honestly it starts to annoy me because it usually isnt the problem. one thing people never seem to say with alt whine is that it could be the amp or hu. i have just changed these out and noticed a big difference is alt whine. it isnt wiring, its just the product.
anyways, look at the engine noise sticky on CA.com and take some notes from it. make this a little better and itll be worth a sticky. as it is, i dont think you go into enough detailed tips.