I have a backup running every night using a program called FBackup. I just recently started Bitcoin mining, and I'd like to have this running overnight as well. This doesn't seem like it should be an issue, as a backup isn't the kind of thing that would use GPU cycles. However, when my backup is running, it drops from around 138Mh/s to 4Mh/s or so. As soon as I pause the backup the speed returns to normal, and as soon as I resume the backup it slows down again, so I know that's what's causing the drop in speed.

Has anyone else experienced this problem? Does anyone know how to fix it? I'm using gui-miner on a GeForce GTX 580.