Noise problem

I am having a small problem with alternator whine that I can't get rid of.  I have a Pioneer dehp-8000  head unit, a four channel rockford fosgate 600x  running a pair of 6 1/2 rockford fosgate mids from a component set and  a pair of 5 1/4 components, and a punch 800a running a single MTX 9500 10' sub.  My engine noise is only in the four channel amp.  If I disconnect either of the two pairs of RCA cables then the noise goes away, but whenever I have both plugged in it is there.  I have switched the RCA cables and temporarily replaced one or the other while using the installed ones on the other side and i still have the same problem.  I have temporarily grounded the head unit at the amplifiers ground to isolate any ground loops, still have the engine noise.  I don't know what else to try.  Could it be bad RCA cables...they are old and have not been used for a while.?  could it be in the amp?   could it be in the head unit?

Any help would be appreciated.

I would say subtle but noticeable, it also changes pitch with RPMs.

I'm experiencing the same problem with a Profile 4-channel amp and don't know what to do.  I was getting a slight whine that also increased it's pitch with RPMs.  I thought to myself, if it's my amp, it will do it even if the RCAs are not plugged in, so I disconnected them and the noise remained.   In my opinion that ruled out the amp.  Then I noticed that if I disconnect only one pair of RCAs the noise disappeared.  This happened with either set on either input.  For example, if I diconnected channels 3/4, the noise from 1/2 went away.  If I took the same RCA's from channels 1/2 and put them into 3/4 leaving 1/2 empty the noise was still not present.  If I did the same process using the other set of RCAs from channels 3/4 I got the same results.  But in either case when the two sets of RCAs were plugged in using 3 or more channels the noise was there. 

If I swapped the RCAs so that the front outputs were connected to the rear inputs and vice versa the whine persisted.  I re-routed the RCAs thinking that my cheap Scosche wires were inviting interference but all that did was make it worse.  It seems like I was right about the wires.  Just to make sure, I hooked up my system so that the amp and HU were directly connected without the RCAs being routed under the rug and so on, and the noise was still there but it would get quieter or louder it I moved them around from one location to another.  At this point I was sure that my cables were the cause of my problems.  I got online and spent $50 on a set of 4-channel Streetwires Zero Noise 3 RCAs thinking to myself, "Wow, fifty bucks. Plus, with a name like that, it's gotta work!" 

I got my RCAs a few days later and quickly went to the car to put them in.  As soon as I started the car I became instantly disappointed when I heard that the whine was still there.  So now I'm thinking to myself maybe my HU isn't grounded to a good spot.  Even though it seems like such an easy task, I won't have time start it until this weekend.  Since the whine is loud enough to piss me off, again I thought to myself, " OK, I'll just disconnect channels 3/4 in the meantime so I won't hear the whine.  To my surprise, even with those disconnected, the noise still stuck around.  I did the same troubleshooting process that I did before to isolate the bad wires but now the noise was present on every channel with every wire, even if only one of them was connected unlike before when it was only present when 3 or more channels were connected.  

This still sounds like an RCA cable problem but I don't want to rule out the chance of my amp or HU being bad or maybe just bad grounds on the components.  I have my 4 channel amp and my sub amp hooked up to the same ground location and I don't hear a whine on my sub but that may have something to do with the low-pass filter on the amp.  I already spent big bucks on the RCA cables and would like to avoid spending more money to upgrade the "Big 3" just because of the fear of the upgrade being inaffective to my specific problems.  I have made mute plugs and put them on all four inputs on my amp and I did not get a whine, but then again, I don't get any noise when there are no cables installed so I'm not quite sure what to me of this information.  Maybe someone with grand experience will be able to make something of my findings and maybe give me some information on how to fix it or further troubleshoot the problem.    Thanks for looking and sorry for such a long post.