VTX3D Radeon 6770 problem

First of all hello to everyone
Now,to the topic.
For the last couple of days I have been playing Battlefield 3 and Deux Ex - Human Revolution(both in DX 11 )and every time the picture on my LCD screen is darker I can see these faint white wavy horizontal lines that go up and down.Now,this is not exactly game breaking or anything but I am just concerned that my gfx card is maybe overheating and causing these symptoms.I measured the temperature through HWMonitor Pro and it is around 43 degrees(Celsius)at idle and maximum under load while playing BF3 is 79 degrees.So,what do you guys think what could be causing this?
My PC specifications are:
CPU:AMD Athlon II X3 455 3,3G Hz
RAM:4GB DDR2 800 MHz
GPU:VTX3D Radeon 6770 1 GB DDR5
PSU:Seasonic 520 W

Sounds like it could be an overheating isssue.I would clean the card off with some dust-off to see if this helps...if its already been cleaned and or new...try leaving the side off the case would also try updating the drivers if you haven't alreaady.You could also roll back the drivers if you've never has this prob.
Through experience I 've noticed some cards don't like as much heat as stated in reviews or specs.
Had a 7900 GT back in the day that would NOT play well over 50* cels

Nope,just tested it with the side of the case open it's not the overheating maybe it's the direct x 11 problem,btw I thought that this is a ATI video card forum?