Same thing happened again... upon powering up Mr. SDE today a horrible noise emanated from the Audio outs. Popped the case open and attempted the same fix as last time by re-seating the PROMS and connectors and in so doing found the cause to be a loose fitting connector on the Power Supply side of the 8 wire Ribbon Cable that spans over to the Motherboard. Carefully bending the pins just a little to create some friction against the connector contacts solved it, although a better solution would be to build a new Ribbon Cable with new and better fitting contacts. Also, cleaning the pins with electronic contact cleaner goes without saying..