First of all disable Intel SpeedStep Technology. And instead of using CPU Voltage in offset mode, use manual. Then you find true stable core voltage, then you can play around with offset. Also you might want to enable Package C-state support, it might help to stabilyze on idle. In my case it did, but the C1E must be disabled. And lastly, try using High Performance power plan in windows power settings. You can enable on balance then you find stable clock and voltage and will use offset voltage, but for now, just try to do that and see if it helps.