Yeah, plug them both in. As ThatJoe rightly suggested, the 8800 will squeal when they have low power, it also happens for a split second when you shut down the system for some people as the PSU cuts the power to the graphics card then shuts the system off, and for that little bit of time the squeal happens, in case you wonder about that too.ps dya need both the pci-e cable in the 8800gtx?