The only way I found working:

// Hide the grid when it is visible.
if ( $('#yourtableid).getGridParam('gridstate') == 'visible') {
   $('#gview_yourtableid a.ui-jqgrid-titlebar-close.HeaderButton').trigger('click');
}

Any other thoughts on this are more than welcome!

Couldn’t find a jqGrid function to do it “properly” from outside the grid.
Setting the gridstate and refreshing didn’t work ?!?