bad ground?

I hear engine noise through my tower speakers when the boat is running. As the engine revs and the rpms go higher the high pitch from the tower speakers also gets louder. This noise only comes from the tower speakers, not the in boat speakers. When the boat is off and the stero is on the speakers play fine and so high pitch noise is generated. The tower speakers are run off of a kenwood amp and the boat speakers seem to be ran straight from the head unit. I have a 05 24' sunsport. I have taken all the speakers out of the roswell tower to inspect the wiring and they all have solid connections. The amp is also grounded directly to the battery so I don't see this as being the reason. What else could be causing the noise?

check and see where the battery is grounded to and make sure its clean and not corroded. You can also try a ground loop isolator. Any audio shop should have one.

Do any wires that go to the speakers, run with any large diameter wiring from the alternator or the battery? Especially the RCA wire from the headunit to the amp

I dont think the battery is grounded to anything. It is just sitting there but all the connections on tje battery are tight and there are no signs of corrosion.
As fas as the wiring goes i will have to check on that. I dont think the speaker wires are running with any other wires but i will still double check. I know that if they have to cross it should be done at a 90 degree angle.
I havent checked anything with the hwad unit. Could a lose wire there somehow cause the noise?

The noise is most likely coming from the battery which is causing a ground loop. Just like in cars you do not want to ground to battery it is always better to use alternator ground or chassis, but in a boat you don’t have that luxury. So I would do what kracker said and check all connections first then get ground loop isolator. If your speaker wires or RCA wires come into contact with power wires and the insulation is not good you will get engine noise. I have used some split loom before and it helps to insulate the power wire or speaker wires.

I had the same issue other than i was getting the noice through all of my speakers but ran from 2 separate amps. I exhausted all options shielded RCA's, routing options with power and ground to amps. It turned out even with the head unit grounded it was not good enough, i ended up taking the ground wire out of the head unit which was grounded to a screw in the boat and taking it directly to the negative battery to get the best ground, eliminated all engine noise, fought it for a year....Good luck!!!

Does your boat have a single or dual battery setup?