Whistling noise coming from fan?

[squarehead94]

Hey guys, Got my prolimatech genesis dual orangeline edition cpu cooler, it has some nice orange fans on it.
However, I think this is coming from my top fan, there is a whistling noise coming from it, after around 20 minutes of use on my pc. It is noticeably loud, and I am curious as to what it is as it doesn't usually do it, only after my pc has been running for a period of time.

any ideas?

 

[Uncle Petey]

Are you sure it's the cooler fan and not the rear exhaust?
Only reason I ask is that case grills can generate whistling as air rushes through.
Is the cooler fan mounted the right way? (Air going to the rear of the case). If not, having the face of the fan against a heatsink can cause undesirable noise in some situations.

Are those fans PWM and set to auto adjust?

 

[squarehead94]

its a prolimatech genesis dual orangeline cooler, my case is odd its a RV02 raven case, so the board is at the top of the case, so my exhaust fan is at the top. I have an exhaust fan and its around 4 inches from the top of the cooler. its only occassionally i hear the whine but sometimes its loud.