I have the same issue with an MBP Early-2011. The LocigBoard had been changed some months ago, and since some weeks I have that flickering as well, it gets worse and worse.
@gary lewis & oldturkey03:
I found some picture of the possibly related Philips head screw mentioned in gary's post. Have a look here:
https://discussions.apple.com/message/19894113#19894113
is that the mentioned screw?