The "whirring" noise? Sounds pulley or belt related. Maybe an idler or tensioner pulley? Won't know for sure until you do some diagnosis. You can remove the belt and see if the noise goes away... that's usually the first step.

Or, you could try spraying some WD40 on the belt and pulleys to see if the noise changes tone or goes away completely. You should clean the WD40 off after the test.

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