Sounds like a fan. Check all your fans when it's happening. On occasion the clip that hold the fan blades in place over the bearings will wear out or break. For example, Foxconn had an issue with newer ones that were not properly lubed in one of their asian facilities. Dell ended up with mass replacements of CPU fans on Optiplex towers because of rusted clips. When the clip breaks, the spring that holds the fan in place pushes the fan up a small bit against the fan housing, or allows the brushes to wear tightly against the bushings. when the brushes & bushings wear out, the fan can seize up. Usually the noise means it could seize up sometimes soon.
Check first to make sure it's not a cable that occasionally rubs against the fan. When the noise is happening, you can try tapping the center of the fan to see if it increases in noise, or temporarily stops the noise. If this is the issue, replace the fan. They are pretty cheap. If this system is new, you can see if they will send you a replacement under warranty.