Question about the struts on my 2005 Chevy Malibu?

I'm driving a 2005 Chevy Malibu. We bought it with 16000 miles on it, it used to be a rental. We had no problems with it except for an annoying bumping noise. We had the car aligned, tires changed, brakes checked/changed and we kept hearing it any time we go above 35mph. The sound stops when I turn the wheel slightly either way or slow down to below 35. Also, when the car goes over a bump, such as a speed bump or even a moderate road bump (even at slow speeds) I hear a sound like air escaping very quickly, like a PSHH! squeak sound. It sounds like a combination of the PSHH and a squeak, that's the best I can describe it. I can't tell which side it's coming from but it's loud, especially with the windows down. I thought it was normal since the car has always done it, and never associated it with the bumping noise. We've had absolutely no trouble with the car for 4 years except for this, and it's VERY annoying. No one has been able to figure it out, but I'm taking it to be looked at tomorrow. Does it sound like it could be the front end struts? How much would that cost average in North Carolina?Question about the struts on my 2005 Chevy Malibu?either the struts or wheel bearing loose. it also could be the sway bar bushings worn out and hitting on metal.