Just to give an update on this, I also have the same issue in Windows 7 32bit (GeForce 8600GT and GeForce 220 both), but only when mIRC is maximized (Aero Glass is on, btw). I can see the flickering icons through the transparent titlebar even when not doing anything. This only happens shortly after maximizing mIRC, though. Maybe mIRC's displaying all of the windows I have open and that causes it? I don't know (I keep all windows in mIRC maximized if that helps). After it's been up and running without anything on top of it, it never does it again until I maximize it again at some later time.
