The despicable whine noise.

I assume you have an external amplifier connected to the head unit, hence the use of the RCA ground loop filters. 

Noise can occur when the signal grounding path is broken or duplicated by a chassis grounding path.  The duplicate path can occur if the amp is screwed to metal directly ( i mount them to wood to insulate them).  Some amps do a better job of rejecting ground loops than others.  Sometimes, signal grounds need to be added.

The audio system has chassis grounds and signal grounds. 

Chassis grounds connect to outer metal and primarily provide a voltage reference for the power supply.

Signal grounds are voltage references within the audio signal path and may or may not connect intentionally to chassis grounds.

When we identify a ground loop, we are saying that there is unintentional current on the signal ground that should be on the chassis ground.

Another issue is a floating signal ground in which the signal ground path is broken and looks like an antenna to the preamp circuit.

ok,  thanks for bringing this up.  I would suggest you have to ground your head units RCA to the head unit chassis as the RCA's themselves have poor internal grounding. 

This is how you do it....  you will have to open the front panels to access the rear of your head unit where the RCA'S plug into the source unit.  Then you remove the RCA's, tag the RCA's so you know its front, rear, subwoofer.    Take , a strand of speaker wire and splice it to reveal the copper wires,  splice enough so you will have to twirl the wires in a figure 8 shape around a pair of RCA,s go around the RCA inputs behind the head unit, then apply solder to get the figure 8 shape.  You may have to do this to each RCA inputs that run to your amps, so if you have two or three running, you will have to do all three :blackeye:

Then solder all of them to one wire and use a stock screw point on your head unit to "ground" them.  Then insert your RCA's back.  Make sure the ground figure 8 goes first in the RCA port, then the RCA's should slide in to secure them.

You can connect the source power wire and test it before you put it all back in.  Hopefully this should solve your engine noise or any ground loop issue.

Let me know how you go mate!

for an image of the above process, google "pioneer head unit rca grounding" 

pics like this come up: