When your vehicle makes a high pitched squeal that is intermittent the most common cause is the wear indicator on the brake pads.
When the brake pads get worn down enough to need replaced the wear indicator which is made of metal is designed to touch the rotor and make a squealing noise to alert the driver that the brake pads need replaced.
If the squealing sound stops when you apply the brakes then it's most certainly the brake pads wear indicator causing the squeal noise.
If it's not that then it could be your wheels being misaligned or the brake pads are vibrating.
If you're uncomfortable working with the brakes then you should take the car to a brake shop and have them inspect the brakes and tell them about the squealing problem as well.