I have never seen this problem, but a search has revealed similar problems associated with bad connections between the motherboard and screen and between hardware and the motherboard; this seems to link in with your comment that it "seems to be related to disc activity".
I would suggest two options:
If you bought it recently and it is under warranty, take it back.
If it's out of warranty, check all connections, especially those of the HDD.
A interesting point about "related to disc activity", but at the same time you mention that "it does it all the time".
Because on occasions I have a similar problem, which seems to indicate a conflict within the program I am using. Normally this comes about, while I am listening to a cd, and at the same time using the computer. As its only occasional, I haven't really bothered about finding a solution.
The other problem, could be something more sinister of a failing part, so it might pay to see if the 'shivering' expands.
Possibly nothing to do with your problem, but just a thought?.
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