Quote Originally Posted by lewisb13 View Post
Ok so I triple checked, b+ and b- are all on same battery. Jumped the rcas, no change. Turn the gain up or down with no rcas plugged in at all, no change.
Okay, the speaker grounds are common to the RCA shield ground on most topologies. So if you have a grounded wire in the tower harness it can deliver any noise directly to the amplifier input. This might mean that you have a second B+ short in the tower. A tower can conduct. Use a test speaker laying on the floor with a new wire laying on the floor. Disconnect and short the amplifier inputs. Now you are 100% isolated from any audio equipment and wiring in the boat except for the supply. If you still have noise under these conditions, then you have an issue with the amplifier which may be unable to reject the normal noise common to every boat. If the noise disappears then start checking the tower harness. Keep in mind that you cannot read a short on the capacitor-coupled tweeter.