Hi
The bar chart and the line charts have an option at Presentation panel to not show the grid lines "Grid line spacing -> Custom -> No lines".
However, this is not possible on the combo charts. The only possible control is how often they are shown (Scale: Wide, medium, narrow).
This setting is also a must for the combo chart, specially when you are showing dashboards where the combo box is shown together with bar/line charts where grid is removed.
Best regards,
Cristian
Cristian Dorbesi