2007 Edge getting a whistling sound from brakes when first starting off

[Brett-2007]

I'm getting high pitch whistling noisy when I first start my 2007 Ford Edg and have the brake peddle engaged and the transmission is put into reverse. The whistling sound will eventually subside but its continuing to last longer as time pass. The brake peddle doesn't seem to loose pressure .

[thirdgenlxi]

So does it ONLY do it when the brake pedal is pressed and it's in reverse? Or does it all the time when started cold? Often time belts can squeak/squeal when first started cold then go away after a couple minutes