My dragrigidbodies script makes the carried object jittery

Hello guys, i have this script that i did not write myself although i have modified it equally much. It was originally in c# but i converted it to Java. It works perfectly except that when im holding an object still its going back and forth and its jittering in the same place. You guys have any ideas on this?

Heres the code, feel free to use it both for helping me and own use:

 var drag : boolean = false;
 var dragH : boolean = false;
 private var cam : Transform;
 private var dragMark : Transform;
 private var startSpeed : float;
 private var rigid : Rigidbody;
 private var mainCamera : GameObject;
 
 function Start () 
 {
     
     if (GameObject.Find ("DragMark"))
             dragMark = GameObject.Find ("DragMark").transform;
     
     if (Camera.main != null)
             cam = Camera.main.transform;
             
     startSpeed = speed;
 }
 
 function Update () 
 {
     if (dragMark == null || camera == null)
         return;
         
     var ray : Ray = Camera.main.ScreenPointToRay (Input.mousePosition);
     var hit : RaycastHit;
     
     if (Input.GetMouseButtonDown(0))
     {
         if (Physics.Raycast (ray, hit, Mathf.Infinity))
         {
             if (hit.collider.gameObject.tag == "DragLight" && hit.distance <= maxDistance)
             {
                 if (hit.collider.rigidbody != null)
                 {
                     rigid = hit.collider.rigidbody;
                     dragMark.position = rigid.position;
                     drag = true;
                 }
             }
             
             if (hit.collider.gameObject.tag == "DragHeavy" && hit.distance <= maxDistance)
             {
                 //GetComponent(MouseLook).enabled = false;
                 //mainCamera.GetComponent(MouseLook).enabled = false;
                 if (hit.collider.rigidbody != null)
                 {
                     rigid = hit.collider.rigidbody;
                     dragMark.position = rigid.position;
                     rigid.constraints = RigidbodyConstraints.FreezePositionY | RigidbodyConstraints.FreezeRotation;
                     dragH = true;
                 }
             }
         }
     }
     
     if (drag == true && rigid)
     {
         if (Input.GetMouseButtonUp(1) && rigid)
         {
             rigid.rigidbody.AddForce (transform.forward * 1000);
             rigid.constraints = RigidbodyConstraints.None;
             drag = false;
         }
     }
     if (Input.GetMouseButtonUp (0) && rigid) 
     {
         rigid.constraints = RigidbodyConstraints.None;
         drag = false;
         dragH = false;
     }
     
     if (rigid == null || dragH == false && drag == false)
         return;
         
         var dis : float = Vector3.Distance (dragMark.position, rigid.position);
                         dis = Mathf.Clamp (dis, 0, 3);
                         speed = startSpeed * dis / rigid.rigidbody.mass;
 
                         var direction : Vector3 = (dragMark.position - rigid.position).normalized;
                         rigid.velocity = direction * speed;
 
         var disH : float = Vector3.Distance (dragMark.position, rigid.position);
         disH = Mathf.Clamp (disH, 0, 3);
         speedH = startSpeed * disH / rigid.rigidbody.mass;
         
         var directionH : Vector3 = (dragMark.position - rigid.position).normalized;
         rigid.velocity = directionH * speedH;
         
 }