EVGA GTX 560ti SC And FurMark?

I've come across something odd while benchmarking my 560ti prior to trying a bit of overclocking.While using FurMark 1.9.2 for testing, with EVGA's Precision X open for monitoring, the GPU clock bounces between 450 and 900 MHz (with 900 MHz being the default clock on this card). This is very evident on the "furry doughnut" as it moves faster and slower in a rhythmic fashion.I noted the FurMark score, closed Precision X and tried again. Got approximately the same score, so I shut down the machine and rebooted. Ran FurMark again without ever starting Precision X but still got the same results.This GPU clock "oscillation" doesn't occur when I run other tools such as OCCT or Unigine.Is this normal?