directional gyro uncontrolled spinning

The other day I was on a flight using the project airbus A320 from KJFK to KLAS. Using autopilot I noticed that it kept correcting for being off course. Looking at the GPS map I knew I was headed west, but the DG indicated headed south. Then two minutes later, indicated east............the DG kept spinning. I did some troubleshooting. Sitting on the runway 25L at KLAS, heading indicates about 340. Heading on runway 17L at KCOS indicates 250, and in flight the DG keeps slowly spinning. How could this happen? Has anyone come across this issue........whats the fix? Gyro precession is set to off.