Unity Cloud Build can't find extension method, however local build can

I seem to have an issue with Unity Cloud Build where it can't find an extension method. However, when I do a local build, it works just find. Is Util like reserved? I don't believe it's my .gitignore.

Cloud Build Error:

 651: [Unity] -----CompilerOutput:-stdout--exitcode: 1--compilationhadfailure: True--outfile: Temp/Assembly-CSharp.dll
 652: [Unity] Compilation failed: 2 error(s), 0 warnings
 653: [Unity] Assets/Scripts/Player.cs(212,43): error CS1061: Type `UnityEngine.AudioClip[]' does not contain a definition for `RandomElement' and no extension method `RandomElement' of type `UnityEngine.AudioClip[]' could be found. Are you missing an assembly reference?
 654: [Unity] /UNITY_PATH/Unity/Unity-5_5_1f1/Unity.app/Contents/Managed/UnityEngine.dll (Location of the symbol related to previous error)
 655: [Unity] Assets/Scripts/Player.cs(218,41): error CS1061: Type `UnityEngine.AudioClip[]' does not contain a definition for `RandomElement' and no extension method `RandomElement' of type `UnityEngine.AudioClip[]' could be found. Are you missing an assembly reference?
 656: [Unity] /UNITY_PATH/Unity/Unity-5_5_1f1/Unity.app/Contents/Managed/UnityEngine.dll (Location of the symbol related to previous error)
 657: [Unity] - Finished compile Library/ScriptAssemblies/Assembly-CSharp.dll
 658: [Unity] Assets/Scripts/Player.cs(212,43): error CS1061: Type `UnityEngine.AudioClip[]' does not contain a definition for `RandomElement' and no extension method `RandomElement' of type `UnityEngine.AudioClip[]' could be found. Are you missing an assembly reference?
 659: [Unity] (Filename: Assets/Scripts/Player.cs Line: 212)
 660: [Unity] Assets/Scripts/Player.cs(218,41): error CS1061: Type `UnityEngine.AudioClip[]' does not contain a definition for `RandomElement' and no extension method `RandomElement' of type `UnityEngine.AudioClip[]' could be found. Are you missing an assembly reference?

Player:

 namespace MyNamespace
 {
     public class Player : MonoBehaviour
     {
         [Header("Audio")]
         public AudioClip[] footstepClips;
         public AudioClip[] attackClips;
         private AudioSource audioSource;
     
         protected void Awake()
         {
             audioSource = GetComponent<AudioSource>();
         }
     
         public void PlayFootstep()
         {
             if(footstepClips.Length > 0)
                 audioSource.PlayOneShot(footstepClips.RandomElement(), 0.5F);
         }
 
         public void PlayAttack()
         {
             if(attackClips.Length > 0)
                 audioSource.PlayOneShot(attackClips.RandomElement(), 0.5F);
         }
     }
 }

Extension method:

 using UnityEngine;
 
 namespace MyNamespace
 {
     public static class Util
     {
         public static T RandomElement<T>(this T[] values)
         {
             return values[Random.Range(0, values.Length)];
         }
     }
 }