I posted this as well in the 2005-2009 GT mods section as I have had some suspension work done, but i wanted to place it here as well in hopes someone may have some thoughts or answers:

I have a 2006 automatic GT that was lowered about 2 years ago with the standard Steeda springs(not the aggressive racing ones OR the ultralites). In March of this year, I had the stock Ford struts and shocks removed and Tokico D-Specs put in. The car also has an upgraded Steeda panhard bar and billet control arms(MAC brand perhaps, I don't remember). Also, the car has the box type sub-frames(they are blue, which I think are the Granetelli ones). The car always had an ever so slight creaking from the right rear, but it was nothing to write home about. Today, all of a sudden, both the left and right rear of the car decides to sound like I'm driving some 20 year old junker Cadillac. You can hear the creaking backing down straight across the driveway and it's by far the worst when I turn left or right on a street OR when I exit or enter a driveway(where it meets the street). I mean it's downright scary. You cringe when you hear this. This is a daily driver car that gets babied and does not see any racing. I'm going to take it in to the local Mustang shop where I've had all my work done on Monday, but I'd like to hear your thoughts of what this might be? I find it hard to believe this is some sort of body creaking. It wasn't there yesterday and now I have what sounds like some old beat up car.

 

I have a 08 auto gt/cs. I had a similar problem. It kind of sounds like the same thing that was going on with my car. My panhard bar came loose. I was able to fix it and there is no more creaking noise. So check that out.

 

+1 Something you replaced is now loose!