My iMac: a 21" i5 ("Mid 2010"). I connected a really nice new Samsung to run as a 2nd monitor (mini displayport out of my iMac into Samsung's HDMI port). Problem: While my 2nd monitor is connected, I will see an extremely brief horizontal "blip" about 2 or 3 times an hour on my iMac. I powered OFF the 2nd monitor, but the "blip" would still happen! I then UNPLUGGED the 2nd monitor, and the "blip" would still happen! The only way to stop the blip is to physically remove the HDMI cable from my iMac. I decided to try a different monitor. I went and bought a really nice new 24" DELL monitor instead (beautiful monitor by the way!). The Dell has a DVI port in the back, so I had to buy a brand new cable, too (a "MiniDisplayPort to DVI" cable). Unfortunately, even with my new Dell Monitor and new cable, I still get that brief horizontal abberation a few times an hour! Turning the Dell OFF does not help, and unplugging the Dell from the wall outlet doesn't help either. Just like before, the only way to make the "blip" on my iMac stop is to physically remove the MiniDisplayport-to-DVI cable from my iMac. Any ideas?