If you disconnect the RCA inpus to the amp(s) are you still getting the noise? If not, the RCA's are to blame. You should re-route them making sure to keep them away from any power/ground wires and the computer. If the nopise does not go away, than a faulty ground is likely the culprit. I would reground it making sure to use a solid connection to the body and scraping all the paint away from the area where your ring terminal touches the body.
