Unity 300ms performance spikes on editor.

Recently , I'm having some performance spikes on editor.

when I create empty project and play there is a serious performance hit(300ms) on every second as you can see in captured screenshot.

profiler indicates MonoIO.Flush() takes 300ms, I have no idea what it is.

And thing is, this spike is only happening while I grab & move any object is scene view. if I don't touch anything there is no spike.

please help.