Turning off other electronics
on board is a good suggestion, as is trying another radio in your boat. My background is as a Two way radio technician. You could take it to a radio shop to check receiver sensitivity and audio recovery but those simple checks are a good place to start. Icom
units are actually very good and usually test better than most of the Standard Horizon radios. Check out Practical Sailor's reviews
and you will see that for yourself. Radio receivers that are dual conversion, i.e. having a high IF and low IF are more susceptible to being interfered with. That could be something simple such as a clock, GPS
or anything that has an onboard oscillator. Don't throw out your Icom
until you first try to eliminate some things. I hope that helps.