Many people, myself included, are having issues with their Radeon HD 7950 cards (and others I think) where the fan will spin up to 100% every few seconds while the monitor is in standby. See this Youtube video of the issue:
It has now been more than a year since these cards were released, but AMD has not resolved the problem. Are there any plans to do so? I experience the problem on Windows 8 64-bit.