think of the carpc and the amp as 2 glasses of water, and think of the rca cable as a tube running between the glasses. if you take water out of the 'carpc' glass, water is going to rush in from the 'amp' glass to replace it until the water level in each glass is exactly even. and if you were to remove some water from the 'amp' glass, water will again rush in from the 'carpc' glass until everything is even.
that is essentially what is happening with a ground loop, except that one glass is constantly trying to be emptied, and the tube is constantly trying to make up for it.
usually a ground loop is caused by different resistances-- either because one device is using a longer wire to reach a shared ground point, or the ground point connection of a device has a higher resistance then another interconnected devices separate ground point..
the idea that needs to be accomplished is to get both devices evenly matched, so voltage isn't flowing between them-- that voltage is what is causing the whining.
and that is about as far as you should need to know for the methodology to fixing it ground loops are insane little gremlins that pop up whenever they feel like it.. you could just throw a sound system in 'just for a weekend' and won't have a single problem with it no matter how hacked, or i've seen it plenty of times where someone will spend hundreds more then they need to, to make every effort to avoid a ground loop situation, only to end up getting a ground loop..