You should have your bonding system checked. Could be a number of causes, bad shore ground isolator, Inverter not properly wired and so on. Although most people like to blame other boats 9 times out of 10 the problem is on their own boat. blaming someone else is just avoiding doing the work of finding the problem. The fact that you are not near other boats a lot would indicate you have an issue onboard. Check your bonding system with a ohm meter and make sure all the connections are good. if you are using all chain rode try grounding that as well. If you run a inverter or generator a lot that could be a source as well. Try reading up on the subject as there is a ton of info out there. Or you could hire a pro to help just make sure you ask about their experience with this type of thing. Sorry but honestly this is not the type of thing that lends itself well to online trouble shooting, you will get lots of advice but a lot will be wrong as well as a lot being good. hard to filter if you have no experience. Good luck