What is Going on with my 960's Fans?

[Jetfighter808]

 

So I was wondering why my Gigabyte Windforce Edition GTX 960 sounded pretty quiet most of the time but then there were random spikes of fan noise. This has been going on for some time but I can only be bothered to correct it now. I opened MSI Afterburner and looked at the RPM of the fans. As you can see, the graph is extremely choppy even though the fan speed % is pretty smooth (23%) minus the one spike where I forced the fans to run at 80% speed. Strangely, the RPM of the fans actually goes down as I increase the fan speed % as shown by the dip in the tachometer graph. 

 

The fan speed is on auto but why is the RPM changing so frequently and peaking so often?

 

Help would be appreciated,

 

Thanks.