try a few tests to see if you can determine what the trouble seems to be:
test monitor with speakers off but attatched.
test monitor with speakers detatched.
test monitor with speakers on low and high.
test monitor with speakers on moved away from your monitor on low and high.
plug the speakers into a different socket than the computer. repeat tests.
offhand i would say either you have a bad connection/cable. it could also be interference in your signal but i dont think so. do some tests.
I have the problem only when i turn the monitor loud and the flicker amplifies as the volume increases.It does not seem to be effected by the distance of the speakers from the monitor,in the sense, the flicker is consistent whether the speaker is far or near,only to depend on the volume of the speaker as I mentioned.
I am left with trying out the last test, which is to plug into a different socket.
I will try it out and update you on the same.