Brand new car making left front noise

I bought a new 2014 dodge avenger with 15 miles on it two months ago. After a few weeks it started making a noise from the left front tire almost like a whistling noise. I hear it when I accelerate from 10-20 mph and also when I come to a stop also from 20-10 mph. The car is under warranty so I took it to the dealership and they took off the wheel and put it up on a lift and also drove it around and they told me they couldn't find anything wrong with it. A few days later I took it up on a Monday and had one of the mechanics drive around the parking lot with me so I could show him the noise it was making. He heard the noise and I scheduled an appointment for Thursday. When I took the car up there it wasn't making the noise so I told them and they said since it wasn't making the noise it would be hard to pinpoint. Two weeks later it started doing it again. It only happens at slow speeds such as parking lot maneuvers and the noise comes and goes. Almost like it has a mind of its own. I took off my tire myself a myself and looked all around since I thought it was something with the brakes because it almost sounds like something is rubbing but it doesn't make a grinding noise. Anyway the rotor was fine no shiny spots and everything else seemed fine as well. Its a brand new car with 1800 miles on it now. Not sure why its making a noise especially when it comes and goes because its not there all of the time. It's driving me crazy. Please help! !