If the GPU fans are running above 90% in your estimation by looking at them and by their noise but the monitoring programs is showing 28 RPM or slow speeds I suggest you open a Sapphire Support ticket and see if your GPU card needs to be checked or replaced.
Sounds like a faulty Fan speed sensor. Either on the GPU card or possibly on the Motherboard reading the GPU Fan sensor. just guessing though.
See what they believe the problem is or have you run certain tests.
If you use a GPU Stressing software on the GPU card you can check to see what the Fan speed is showing when the GPU is under heavy stress or load. It should be at maximum 100%. If it doesn't then you need to have Sapphire check the GPU card out.
NOTE: The GPU card doesn't just have one Hot spot sensor, But it has several Thermal Sensors throughout the GPU card monitoring hot spots on the GPU card. If any starts or reaches 110C the GPU card will automatically slow down to reduce power thus temperature.