Hi I've read quite a few posts concerning this problem and I am at a
loss.
I just installed a sony xm-d500x for my 2 pioneer subs, and I have a
pioneer gm-6000 for my rear and front speakers. All this connected to
a Kenwood KDC-MP522 head unit. I am getting a terrible alternator
whining noise which increases with the RPM. The whining is only coming
from the front output of the headunit. I tried reversing the 2 rca
cables thinking maybe the cable was the problem, but that didn't help.
The only way the whining stops is by connecting the rear output of the
headunit to the sony amp then, using the output from the amp to the
pioneer amp. The only problem here is that I loose all options from my
headunit for controls since the rear output is driving everything. I
think the problem is the headunit, the rear outputs are directly on
the headunit and the front outputs have a 6" RCA cable.
The headunit is also connected to the original speakers in the front &
back through the spk outputs. Therefore I tried unpluging the cable
from the headunit leading to these speakers thinking that may be the
problem but it didn't help.
I tried connecting the rear output directly to the pioneer amp and the
whining stops. So it leads me to beleive that the problem is really
the front output from the headunit. Are there any other tests I can
do? probably not a ground problem since connecting to rear sounds
good.
I aslo noticed that by connecting the pioneer through the Sony using
the rear outputs the pioneer amp gives out a lot more power than
connecting it to the front output directly. I have the rear set to non
fading on the headunit. But if I put the front fader to max shouldn't
the output be the same as the rear output? By using the front output
it seems I have to bring the volume up to about 25 to get the same
level as when I put the volume to 15 going through the rear output.
Any help appreciated.
Thanks in advance.

Check the amps and HU ground. Sand the metal, make the ground wire
shorter, etc.

Make sure none of your RCA cables are run near a OEM wire harness.
Many OEM wire harness' are run in the door trough. I had a bad noise
because my rca cable sat on top of the oem harness. Moved the cable 2
inches, no noise.

Also, if all that doesn't help, re ground the head unit. Don't use the
ground in the wire harness, ground it to bare metal.

i had whine and installed a stinger ground loop isolator and it sorted
it 100%


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