Sounds like frequency noise. Assuming that you have an aftermarket radio with aftermarket speakers if securing your ground connections do not work get one of these 3 should work....
-Noise filters that connect in line with your rca connections behind your radio
-Ground loop Isolators for the same thing....connect behind the radio
-Lastly bypass stock amp if not done so already
Good Luck and if you need complete wiring diagram for your runner let me know and ill send it over