Wiggle expression

If you want to wiggle a bunch of layers at the same time and maintain their relative position you have two very simple options. Parent all of the layers to a null with wiggle() applied to it or Pre-compose all the layers and apply wiggle to the pre-comp. Most of the time I would use parenting. 

Using an expression would require you to retrieve the difference between the comp center and the position of the layer that is wiggling and add that value to the current layer's position. The expression would look like this:

src=thisComp.layer("Null 1").transform.position;
ofst = src - [thisComp.width/2, thisComp.height/2];
value + ofst;

The expression given by OussK does not work. You could remove the wiggle from the null and a layer containing the expression would still wiggle. Apply the expression to multiple layers and they would all wiggle differently.

You can use this expression 

var mSource = thisComp.layer("Null 1");
var P1 = transform.position.wiggle(5,10);// this this you layer wiggle value:
var P2 = thisComp.layer("Null 1").transform.position;
var P3 = thisComp.layer("Null 1").transform.position.valueAtTime(mSource.inPoint);
P1+P2-P3;

change the Null 1 to your Null name, it will look like this