Correct bug with steam locomotive chuffing sound

Author: peternewell

Source/Orts.Simulation/Simulation/RollingStocks/MSTSSteamLocomotive.cs

@@ -3503,13 +3503,26 @@ private void UpdateFX(float elapsedClockSeconds)
                 // Variable is proportional to angular speed, value of 10 means 1 rotation/second.
                 // If wheel is not slipping then use normal wheel speed, this reduces oscillations in variable1 which causes issues with sounds.
 
-                if (SteamEngines[i].AttachedAxle.IsWheelSlip)
+                if (((Train.TrainType == Train.TRAINTYPE.PLAYER && !Train.Autopilot) || Train.TrainType == Train.TRAINTYPE.AI_PLAYERDRIVEN) && (Simulator.UseAdvancedAdhesion && !Simulator.Settings.SimpleControlPhysics))
                 {
-                    variable[i] = Math.Abs(SteamEngines[i].AttachedAxle.SlipSpeedMpS / SteamEngines[i].AttachedAxle.WheelRadiusM / MathHelper.Pi * 5);
+                    if (SteamEngines[i].AttachedAxle.IsWheelSlip)
+                    {
+                        variable[i] = Math.Abs(SteamEngines[i].AttachedAxle.SlipSpeedMpS / SteamEngines[i].AttachedAxle.WheelRadiusM / MathHelper.Pi * 5);
+                    }
+                    else
+                    {
+                        variable[i] = Math.Abs((float)SteamEngines[i].AttachedAxle.AxleSpeedMpS / SteamEngines[i].AttachedAxle.WheelRadiusM / MathHelper.Pi * 5);
+                    }
                 }
-                else
+                else 
+                // Axle code is not executed if it is an AI train, on Autopilot, or Simple adhesion or simple physics is selected. Hence must use wheelspeed in these instances
                 {
-                    variable[i] = Math.Abs((float)SteamEngines[i].AttachedAxle.AxleSpeedMpS / SteamEngines[i].AttachedAxle.WheelRadiusM / MathHelper.Pi * 5);
+                    if (WheelSlip)
+                        variable[i] = Math.Abs(WheelSpeedSlipMpS / SteamEngines[0].AttachedAxle.WheelRadiusM / MathHelper.Pi * 5);
+                    else
+                    {
+                        variable[i] = Math.Abs(WheelSpeedMpS / SteamEngines[0].AttachedAxle.WheelRadiusM / MathHelper.Pi * 5);
+                    }
                 }
 
                 variable[i] = ThrottlePercent == 0 ? 0 : variable[i];