Mattimus,
Does this happen in just one area or all over? I ask this because if you are on the edge of a chart for a given area it may try to constantly reload the charts.
If this is not the case, have you tried to go back to an older version of the software and see if it happens then?
Some settings to check would be the Chart Detail Level and Chart Select. Let me know what these are set to. Change them around and see if anything changes with the flashing.
If none of the above has any affect, I would imagine it have to be the card slot or something hardware related.
Good Luck and let me know what happens,
Robert