Object is stuttering on rotation

Heres the thing, I have written a code in javascript that will make my player rotate, the problem is when I walk around an object ( such as a tree ) the object that I am walking around appears to be stuttering in both the unity player and in the final .exe. Is this a problem with my code or is it a hardware problem?

Here is the code that I am using for my player movement:

 #pragma strict
 
 var power : float = 20.0;
 
 function Update () {
 
 
 if(Input.GetKey("w")){
 
 rigidbody.AddRelativeForce (0, 0, power);
 
 }
 
 
 if(Input.GetKey("s")){
 
 rigidbody.AddRelativeForce (0, 0, -power);
 
  }
  
  
 if(Input.GetKey("a")){
 
 transform.Rotate (0, -180 * Time.deltaTime ,0);
 
 }
 
 if(Input.GetKey("d")){
 
 transform.Rotate (0, 180 * Time.deltaTime ,0);
 
  }
 
 
 
 }

Thanks in advance.