A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Just to close this off, the problem was due to setting the chart area the same size as the ChartObject size. It needs to be a little smaller. Could be the same issue with the plot vs chart area as well... I just set them all progressively smaller and the problem was fixed.
Its a pity there wasn't some actual specifications available for this type of thing.