Catalyst drivers are notoriously known to leave stuff like registry keys behind when you uninstall them. If you have played around with the AMD OverDrives fan control or MSI Afterburner or similar program the drivers could’ve left registry keys/appdata that force the manual fan control on at 100%. What you should do is open your CCC, go to Performance/AMD Overdrive. Scroll down to the bottom of the Overdrive page and make sure Enable manual fan control is off.
If it’s already off and you’re not using any other programs that fiddle with GPU settings I’d suggest you get a 3rd party program that does a complete clean uninstall of your catalyst drivers and software.