C# Sudoku Generator

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static int[,] grid = new int[9, 9];
        static string s;
        static void Init(ref int[,] grid)
        {
            for (int i = 0; i < 9; i++)
            {
                for (int j = 0; j < 9; j++)
                {
                    grid[i, j] = (i * 3 + i / 3 + j) % 9 + 1;

                }
            }
        }
        static void Draw(ref int[,] grid, out string _s)
        {
            for (int x = 0; x < 9; x++)
            {
                for (int y = 0; y < 9; y++)
                {
                    s += grid[x, y].ToString() + " ";
                }
                s += "\n";
            }
            Console.WriteLine(s);
            _s = s;
            s = "";
        }

        static void ChangeTwoCell(ref int[,] grid, int findValue1, int findValue2)
        {
            int xParm1, yParm1, xParm2, yParm2;
            xParm1 = yParm1 = xParm2 = yParm2 = 0;
            for (int i = 0; i < 9; i += 3)
            {
                for (int k = 0; k < 9; k += 3)
                {
                    for (int j = 0; j < 3; j++)
                    {
                        for (int z = 0; z < 3; z++)
                        {
                            if (grid[i + j, k + z] == findValue1)
                            {
                                xParm1 = i + j;
                                yParm1 = k + z;

                            }
                            if (grid[i + j, k + z] == findValue2)
                            {
                                xParm2 = i + j;
                                yParm2 = k + z;

                            }
                        }
                    }
                    grid[xParm1, yParm1] = findValue2;
                    grid[xParm2, yParm2] = findValue1;
                }
            }
        }

        static void Update(ref int[,] grid, int shuffleLevel)
        {
            for (int repeat = 0; repeat < shuffleLevel; repeat++)
            {
                Random rand = new Random(Guid.NewGuid().GetHashCode());
                Random rand2 = new Random(Guid.NewGuid().GetHashCode());
                ChangeTwoCell(ref grid, rand.Next(1, 9), rand2.Next(1, 9));
            }
        }

        static void Main(string[] args)
        {
            s = "";
            string ç1kt1;
            Init(ref grid);
            Update(ref grid, 10);
            Draw(ref grid, out ç1kt1);
            Console.ReadKey();
        }
    }
}

Hello i have a question about some parts of your code.
First what exactly does your Changetwocell do?
and why do you use Guid.NewGuid().GetHashCode() what other purpose does it have? can you not use the normal Random "name" = new random()

I'm asking this because i'm trying to make a sudoku myself and i'm doin some research about it.

Thanks in advance

Both cases of .Next(1, 9) need to be .Next(1, 10). Otherwise, it leaves a 9 in the top right and bottom left corner of every Sudoku it creates.