wires wrong way round on the speaker terminals can cause this
sorry mate, this ^ is incorrect, switching a speakers polarity in this fashion is quite common in car audio, it simply alters speaker 'phasing'.....
is your powercable running next to your RCA's that can cause an interference sound?
in 99% of cars, running power cable with rca's won't cause any issues, the power supply in the car is DC, and most rca leads are shielded.....
if its easier to run these cables together, then do it....
you need to make a few checks to locate the source of your problem....
firstly;
with the system switched off----remove the rca leads from the amp....
switch the system on as normal;
no noise indicates the problem is before the amp....
noise still present indicates its associated to the amp or its wiring....
secondly;
with system switched off----refit rca leads into the amp.....
remove headunit from the dash, remove the rca leads from the headunit....
now switch system on as normal[
no noise present indicates fault is with the headunit or associated wiring....
noise still present indicates its an rca fault....
if your headunit is a Pioneer, then its probably a blown earth track, this can affect other makes, but its most common in Pioneers.....
a little more info, (as requested), would have saved me all this typing....and quite possibly enabled a better educated guess as to what, or where, your issue is
