speaker whine?
 

I know usually these things come from a grounding issue but maybe someone can point out my mistake. I added 2 6v to my dual 12v system for amps...I put the 2 existing 12v's on perko switch 1 and added the two 6v's to perko switch 2. I wired the grounds on the batteries banks together with 4awg. The system has a pretty audible whine only when the engine is on, then goes away if you turn of the HU or turn off the boat engine (with the stereo still on). Did I miss something in my install? Fyi the boat is brand new and worked fine before the addition.

Had same problem, thought it was ground so i went through and basically rewired the system. Turned out one of the amps was fried. Replaced the amp with a new exile and the problem went away.

sounds like "road noise" as its called in the auto world. Does the pitch change with RPM? I'd separate the grounds on the 2 banks and see if that helps.

Its not like the "road noise" that your referring to where it changes pitch. Its just a steady pitch once the boat and stereo are turned on at the same time. At the moment it seems to be gone after I adjusted and tightened some connections so hopefully that was the issue.

Start with the grounds
after that move to the equipment, disconnect stuff until it goes away, then reconnect stuff and narrow it down. I have seen this be bad grounds, bad amps, and even bad speakers or wiring. Just a bunch of trial and error. BTW: You did hook your 6v batteries up to produce 12v right? Stupid question, but something that may be overlooked. If you have it hooked up as a 6v ground system and the rest is setup as a 12v ground system, I could see that giving you some issues. Break out the multimeter and double check.