CPU heat sink fan whining noise. Is it bad?

[Ego Banana]

I'm using a dell xps 435t and I've been hearing a strange whining noise coming from the heat sink occasionally when playing games or when the cpu usage reaches around 14% or above. It doesn't happen for long but I'm just wondering what might be causing it.
(This computer is about 4 years old.)

 

[zink1701]

Usual cause for that is the fan bearings or fan slipping (caused when the fan suddenly speeds up), over time it will only get worse. Do not use lubricant or grease ect on the CPU fan as you risk damage to other components. Only option is to replace the CPU cooler. Make sure it is that before spending any money. Remove the case side when system is off then boot the machine. Run prime95 (CPU torture test) and listen in on the machine. This will elimate the GPU fan if applicable. Hyper evo212 is a good low cost cooler.

 

[Ego Banana]

Thank you for the help. I've recently upgraded to a gtx 750 ti so i'm certain it's not the GPU. Unfortunately the xps 435t requires a custom heat sink so I might have to get a refurbished heat sink.