Tick Problem with Overlay

Hey i simply want to add a String as Overlay ... In the past i simply put the Font Renderer in the onTickinGame and everything was fine but now the String is flickering. Where is my mistake?

package dahappy.minecraft.LandInfo;
import java.util.EnumSet;

import cpw.mods.fml.common.ITickHandler;
import cpw.mods.fml.common.TickType;
import net.minecraft.client.Minecraft;
import net.minecraft.client.gui.GuiScreen;

public class Ticker implements ITickHandler {

@Override
public void tickStart(EnumSet<TickType> type, Object... tickData) {
	// TODO Auto-generated method stub

}

@Override
public void tickEnd(EnumSet<TickType> type, Object... tickData) {
	// TODO Auto-generated method stub
	if(type.equals(EnumSet.of(TickType.CLIENT)))
	  {
	   GuiScreen curScreen = Minecraft.getMinecraft().currentScreen;
	   if(curScreen != null)
	   {
	        onTickInGui();
	   }
	   else onTickInGame();
	  }
}

@Override
public EnumSet<TickType> ticks() {
	// TODO Auto-generated method stub
	return EnumSet.of(TickType.CLIENT);
}

@Override
public String getLabel() {
	// TODO Auto-generated method stub
	return null;
}

private void onTickInGame()
{
	mc.fontRenderer.drawString("Test", sr.getScaledWidth()/2-mc.fontRenderer.getStringWidth(str)/2, 10, 0xff00FF00);
}
private void onTickInGui()
{
   //do stuff out of the world...
}



}