I am hearing a weird noise coming from the back of my car. It's an 05 GT and has an OR/H with borla atak mufflers. I'm thinking it may be vibration or something? Because the h pipe is newly installed. The sound can be heard a lot of the times on a cold start or when I down shift 2 second while doing about 40. The sound almost sounds like a fat person getting out of a screechy bed. It's like a screech noise almost like what shocks sometimes make if your going over a bump or something but it makes the noise while sitting still so it isn't my shocks.. Any idea what this could be? A friend suggested wheel bearings?