An Insanely Annoying Squeal

[RedlineRacer]

This just started for no reason the other day. I am driving to work and I suddenly hear this really annoying high pitch squeal coming from my passenger side outside my car. At first it only sounded when I hit my brakes, so I thought nothing of it, because I just need new brake pads soon. Then, after driving around for about 5 more minutes, it starts making noise when I dont hit the brakes. Now I think it is my rotor shield behind the rotor. So, I pull over at a gas station and look at the shield to see if it might be touching the rotor anywhere. It appeared to be ok, on both sides. Now I am baffled. I am going to spend some time tomorrow taking my wheels off and checking the rotors and brake pads. Is it possible that my caliper pistons could be stuck a little and not retracting totally so it is barely touching my rotor?