Mine was making the noise when really getting on the throttle and when I would shift gears it would squeal like hell. Drove me nucking futs and sounded like garbage. Hey dad check out that sweet mustang all the sudden screetch screetch screetch LOL. You can't really see the metal guard due to the radiator hoses in the way but it's there just pull off your air induction where you can get to the power steering pump pulley and stick your hand down there and feel around, find the guard and bend it up by hand and see if it takes the noise away. I knew the noise was a belt squeal because I had my wife rev the car for me while I looked under the hood but I couldn't really pinpoint the noise due to the echoing that's why I wasted all that money on idler pulleys and then tensioner pulleys and a new serpentine belt and still the squeal so I went put the belt back on one day after looking it over and noticed it was a really tight fit to squeeze the belt between the pulley and the guard. Bent the guard up no more noise.
Black 2005 GT 4.6L 3v SOHC 5-speed, 3.55's k&n drop in