Interference...
If that happen at the dock site, some radio activity may generated that kind of problem.Why don't try with other radio first, connected to the same antenna. A walkie T will be ideal for that test. If you get the same result with it, almost for sure is an outside source. If you get it under way, I will say your radio need a check out in the mixing section. Feel free to e-mail me.Aldo, WA2ISTalozano@monmouth.com