99 Sentra w/ Low whistling noise

I have a 99 Nissan Sentra GXE 1.6 liter w/ 150,000 miles.

I just bought this car last week so I don't know its history. When I accelerate there is a low whistling noise. It is intermittent and once it hit about 30 mph it stops. It only happens at low speeds and I think it gets louder when I turn at low seeds. But like I said, it is not constant, it kind of comes and goes. It's usually worse right as I start driving. The longer I drive the less it happens.
Without being able to hear the noise it really makes it tough to pin down. It can be a lot of things...

1st thing I would want to know is if the car has to be moving or not to make this noise?

A couple of possibilities for both scenarios. If it has to be moving, see if pressing the brk pedal makes it go away, if it does, check your pads, a wear sensor could just barely be hitting the rotor.

If it does it all the time, check your belts, turn the wheel all the way to one side & hold it for a second or 2, if the noise gets really loud, you have a loose or bad belt..........
Yes, the car has to be moving. It only happens when I begin to accelerate. And once Ive been driving for a few miles really doesn't make the noise anymore. I'll try the brake thing and see if that works.

Thank you for your help!
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