Auto body repair & detailing: sound in my car, ponitic, pullys

Question
i have a ponitic grand am 1999 and i brought it used. so im hearing a sound that sounds like a hissing sound. i thought it was the fan belt but it wasnt. so do you think it was a water pump or one of the pullys not turning right, or the A/C unit isnt clicking right. but the funny thing is when im driving i dont hardly hear it but 10 minutes later it get so loud. Why

Answer
Brittany....... you say the hissing sound gets louder after 10 minutes of driving....ok
are you driving at a higher rate of speed 10 minutes later or do you hear the hissing noise while at a stop?

If the hissing noise is loud at 50mph and decreases in sound when you go slower you may have an air leak at one of your doors.

If you hear the noise at any speed then you have to pinpoint it a little better...does the noise come from the engine compartment? Open your hood and then start the car....walk around to the engine compartment and listen for the noise.