Jagsare1,
Most likely what is happening is a over rasterized radar image because the scale does not match that of the chart. This will happen when you are zoomed in on the chart at close ranges and you have the radar set to a range that is much longer. For example you have a 300 yard range on your chart plotter and the radar range is set to 12 milles. You can fix the issue a couple of ways. One when you use the radar overlay make sure the radar is set approximately the same range as the chart range. We also have a toggle button in the radar menu called "range link" this will automatically scale the chart and radar to the same range.
C-bass