Hello and welcome to the forums
If by flickering you mean some lines appearing in 2D mode,then yes i have the same problems too(sometimes),its said that Cat 10.4 will completely take care of this problem and for now,you can raise the 2D clock to 400/900(default is 157/300) and for me it worked,here is how:
1_Open CCC and choose Overdrive tab,unlock the settings(by clicking on the " Gold Key" icon)
2_Go top options,profile and choose profile manager.
3_In the composition tab,choose "The following settings" and in the "ATI Radeon HD 5900 series"make sure only ATI overdrive is checked.
Then enter a profile name,then save and close it(Do not activate).
4_Go to C:\Users\Your UserName\AppData\Local\ATI\ACE\Profiles (Its hidden so make sure you unlock hidden files and folders)
5_Open the profile with wordpad and do this edits:
<Property name="Want_0" value="40000" /> (default is 15700)
<Property name="Want_0" value="90000" /> (default is 30000)