din=framesToTime(effect("durationIn")("Slider"))
don=framesToTime(effect("durationOut")("Slider"))

seedRandom(index,false);
initVal=0;
endVal=100;
wendVal =wiggle(freq,amp)

if (marker.numKeys > 1){
t1 = marker.key("in").time;
t2 = marker.key("out").time;

animateIn = ease(time,t1,t1+din, initVal,endVal);
animateInFlickr = ease(time,t1,t1+din, initVal,wendVal);
animateOut= ease(time,t2+don,t2,endVal,initVal);
animateOutFlickr=ease(time,t2+don,t2,wendVal,initVal);

if (time < (t1+t2)/2)
if(time>=don){endVal}else{
if(effect("flickr in")("Checkbox")==true)
{ animateInFlickr;}else{animateIn;}}

else{
if(time

I know it's messy and dirty, if any expression meister here could tidy up the code maybe it can look better, buuut anyway now it works...

//

You can also add an extra nice pulse opacity effect linking the endVal to a slider. You should also add a checkbox, and this code on the slider (which can be called endVal)


freq = 5;
amp = 3;
base = 90;
innerPulse=base + amp*Math.sin(freq*time*Math.PI*2)

if(effect("innerPulse")("Checkbox")==true){
innerPulse;}else{value}

so when the checkbox is on, there will be a pulse between the "in" and "out" markers, but if checkbox is off, just the value at the slider. Of course the more sliders you link paramerers to, more options you will have in order to animate, but it can get a bit messy on the Effect Controls (I'd use Pseudo Effects to have it less messy)
happy flickering!