A pop up keeps appearing and disappearing
I keep seeing a Pop Up that pops up and disappears again for a split second on my screen.
It's so fast, I can't tell what it is, but it looks like a warning dialog box.
It pops up at random times. It doesn't matter what windows or finders I have open.
Sometimes it appears when I'm surfing youtube or ebay, others when I'm watching movies or streaming videos online....
The problem is, It disappears before I get the chance to see what it is or deal with it. (It's gone before I can even screen shot it).
It's been happening for a few weeks now and even after updating, it's still there.... I get the feeling it's slowing down my system some what too...
Any ideas what it may be or how I can go about finding out? and potentially removing it?
Thanks guys and girls.
MacBook Pro, OS X Mountain Lion (10.8.2)