Windows 7: Noticed monitor vibrating last night.

Noticed for the first time last night.

Set Windows Media Center to record Hawaii 5-0. So it goes off as usual, I come back to the PC, turn o nthe monitor, and I notice; picture in blurry due to so much very fast back & forth vibrating. Looked like the monitor was acutally blurry or distorted. Wasn't the browser- the desktop looked the same. When I went to bed at 930 I didn't look like this- when I came back @ 1035 it did...I went back again 10 min later, and it was gone. File recorded perfectly, no distortion. Haven't introduced any new electronics in the area to cause conflict.

Any ideas? Outside interference? For the record I have a 2011 HP h8-1010t with Windows 7 home prem.
Checked device manager, all OK.