Alternator Whine: HELP!

[amagalla]

I'm totally confused. I though I had eliminated the alternator As the source of the whine. Here was my process:

With the engine running (hearing the whine), I disconnect the RCA cables. The noise goes away.

But now, during my testing process, with the engine running (hearing the whine), I disconnect the battery positive lead (the amp + is connected to it as well) leaving the engine (and the head unit) running on just the alternator. I then connect the positive of the amp to the battery + lead leaving the amp powered by the battery...Presto, engine running an no whine.

So, how do I solve this? Do I need a big amp capacitor (normally used for big bass installs)? Will this solve the issue?

Thanks.

Tony