I have the power cable from running on the drivers side of the car. The speaker wirers are running in the middle and the RCAs are run on the passenger side.
Like Chum said making sure the rest of your install is proper first may fix your issue. $100 RCA's does not a noiseless system make. More often than not a difference in ground potential will allow noise into a system far easier than an 'inferior' set of signal cables. Where and how are your components grounded - Radio? Amp(s)? etc. I would bet if you put an ohmmeter between your radio ground and amp ground you would be surprised at how much of a difference there is. Begin by regrounding your HU securely to some bare metal (scraped or wire brushed til shiny) and do the same to your amp(s). Follow up by cleaning up wiring under the hood (big 6 etc) and go from there. You may fix your noise problem and help your system's electrical demands all at the same time. If the noise is still there, atleast you know that everything else is done right.
Remember, low level signal needs to stay far away from high current power as possible and when necessary crossed at 90* angles...this means ALL high current (computer modules, heater wires, blower motors etc.).