Ditto to what Chuck said about metal near the fluxgate compass. after we moved all our "stuff" onto our, new to us, boat it would not track but kept hunting all over the place. Several folks suggested that problem. After a long search for the compass, I had no idea where it was, I found it back to back with our shopvac with only a plywood bulkhead separating them. We moved the vac. and it fixed the problem in that case.
Steve