You didn't say anything about your system, but have you updated to the latest firmware for your drive? It could be the quality of the disks or a problem with DLA. Do you have DMA enabled for your drive. There are a lot of variables. Is your power supply adequate for your peripherals?
Try updating your firmware. If the drive shares the controller with a hard drive, put it on the secondary controller and set it as Master. Make sure DMA is enabled. Usually, if you set your bios to Auto, it will configure the drive right. What OS do you use? These are just a few things to consider.
Of course, your drive could be on the way out. Do a self-diagnostic as described in your manual.