2000 Dodge Intrepid High Pitched Squealing

Well it's had a high pitched noise for quite a while now. It started mainly when I braked under 20 miles an hour. I figured it was just the brakes. Well about a month later the Check Engine Light came on and I took it to auto zone where the computer told me it was either a catalytic converter or a fuel problem (separate problem). I used fuel cleaner and it hasnt went out yet. Since that problem happened though the squealing noise has gotten worse and practically does it all the time now regardless of whether I brake or not. It mainly squeals worse when I am accelerating. I noticed just messing around though if I hold the brake slightly while im accelerating it doesn't make the noise nearly as loud. Am I looking at a brake problem or possibly something more serious?