This was one of the problems that drove me insane for about a year and it almost made me limit my lighting until one day i found a solution.
Turn up the dmap resolution and secondly turn off 'Dmap autofocus' in the shadow properties.
Most of us ignore this value and leave it at its default but that is the main culprit behind flickering lights and shadows.
The idea is to balance the dmap resolution and the dmap autofocus value.
Start with a low autofocus value e.g 40 and test your results.
This should definitely fix the problem.