Did you measure your ground and hot connections for low resistance?
There is pictures of my power routing in the above link.
I never had noise issues with the OEM setup so if the problem was there
to begin with I don't really know the solution, but I have seen the noise issue
come up here before with this identical setup.
Since the amp is a switching type I would have kept the crossovers away from the amp but that
might just be superstition on my part.
See #6 in the last link provided in the last post ,(not this post). the troubleshooting link