ATI Radeon hd5770 fan speed faster with open source driver

My ATI radeon hd5770 fan speed runs faster in open suse 11.4 with the radeon driver than it did in ubuntu 10.10 with the ATI proprietary catalyst driver. I just wondered if this is normal? I am using the hardware temperature widget included on the desktop it shows the card running at 159 degrees Fahrenheit. Everything seems to be working ok is this something to be concerned about?