I have a slc dc reel and am getting a backlash everytime i cast no matter what setting i use I did take the cover off and was wondering If I have to put the cover back on at a certain setting 1,2,3 or 4  any help would be welcome i am using 10 lb mono line but have also tried braided line with the same result

Do you have the spool tension knob too loose?

Check your spool tension knob. I had the same issue with my curado dc as I tried setting it up like my Daiwa reels instead of reading the instructions and setting it up correctly. Once I had the spool tension adjusted correctly the issue went away and I've had no further problems with it. 

What lure are you using and what is the weight?

 

Some tips without knowing what you are using:

 

Shimano says to adjust the cast control knob until you feel little to no side to side motion when moving the spool with your fingers. 
 

You can and should adjust the cast control knob like you would any baitcaster the first time out. Adjust tension until your bait falls slowly. Then put the side adjustment to 4. At this point you can cast without backlash but won’t get much distance. When you are comfortable then you can go down to 3, 2 and eventually 1. 

Settings 

1 lowest braking 

2 mono or braid

3 fluro

4 max brake-wind or awkward lures

 

dont set the spool tight or the dc won’t work properly… just tight enough to get rid of the spool side to side play . This is per shimano and there’s a informative YouTube video from jp derose about all of this .  Dc isn’t a cute all either and often you’ll need to thumb it here and there, especially when the lure hits the water or you could get a backlash still.  Or maybe perhaps you got a bad one or just need to work on your casting skills …. 

What line, lure, and rod and how hard are you trying to chuck it.

I could blow mine up every time by trying to throw too hard with a light bait.

I would guess that the spool tension is loose and or you have the brakes on on a lighter setting then you should.

Is the reel spooled to the correct level?  Too much or too little line mine will behave badly. 

If you're used to casting spinning tackle, there's a tendency to jerk with your wrist - it's rewarded with distance in spinning tackle. 

Casting a baitcaster has to be a smoother start - all jerk you add to the cast is only start-up backlash.